Organic Acid: notes and MCQs for State PSC prelims

Organic Acid is part of Chemistry. Below are notes on 8 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Acidity of Carboxylic Acids: Factors Affecting Acidity (Inductive, Resonance Effects, pKa Values)

Acidity of carboxylic acids depends on the stability of the carboxylate anion (RCOO⁻) formed after proton (H⁺) donation.
Carboxylate anion is resonance stabilized by delocalizing the negative charge over two equivalent oxygen atoms, making carboxylic acids much stronger acids than alcohols and phenols (which have less effective or no resonance stabilization).
Electron-Withdrawing Groups (EWGs) increase acidity by stabilizing the carboxylate anion (dispersing negative charge) through -I (inductive) and/or -R (resonance) effects.
Electron-Donating Groups (EDGs) decrease acidity by destabilizing the carboxylate anion (concentrating negative charge) through +I (inductive) and/or +R (resonance) effects.
Inductive Effect: Decreases with increasing distance of the substituent from the carboxyl group.
pKa Value: A lower pKa value indicates a stronger acid.
Comparison of Aliphatic Carboxylic Acids: Acidity decreases as the length of the alkyl chain (EDG, +I effect) increases: HCOOH (Formic acid) > CH₃COOH (Acetic acid) > C₂H₅COOH > C₃H₇COOH.
Effect of Halogens: Acidity increases with the electronegativity of the halogen and the number of halogen atoms. E.g., FCH₂COOH > ClCH₂COOH > BrCH₂COOH; CCl₃COOH > CHCl₂COOH > CH₂ClCOOH.
Order of EWG Strength (Acidity): Stronger EWGs lead to stronger acids. For example, based on pKa values: CF₃COOH (pKa ≈

CH₂COOH (pKa ≈ 1.68) > NC-CH₂COOH (pKa ≈ 2.46).

Solubility: Simple aliphatic carboxylic acids (up to 4-5 carbons) are soluble in water due to hydrogen bonding. Higher carboxylic acids are practically insoluble in water due to the dominant hydrophobic hydrocarbon part.
pKa of Acetic Acid: Approximately 4.76.
Acidity Order Comparison (Phenol, Benzoic acid, p-Nitrophenol): Benzoic acid (pKa ≈

(pKa ≈ 10.0). Carboxylic acids are generally stronger than phenols. EWGs (-NO₂) significantly increase phenol acidity.

Picric Acid (2,4,6-trinitrophenol): An exceptionally strong acid (pKa ≈ 0.38), stronger than most carboxylic acids (including benzoic acid), due to the strong electron-withdrawing and resonance stabilization by three nitro groups.
Salicylic Acid (o-hydroxybenzoic acid): Stronger than benzoic acid due to intramolecular hydrogen bonding in its carboxylate anion, which stabilizes it, and the -I effect of the hydroxyl group.
o-Toluic Acid (o-methylbenzoic acid): Weaker than benzoic acid due to the electrondonating (+I effect) methyl group.

Aromatic Carboxylic Acids: Benzoic Acid, Salicylic Acid (Preparation, Properties, Reactions)

Aromatic Carboxylic Acids: Organic compounds containing a carboxyl group (COOH) directly attached to an aromatic ring.
Benzoic Acid (C6H5COOH):
Preparation:

Oxidation of Toluene: By strong oxidizing agents like alkaline KMnO₄ or acidic K₂Cr₂O₇/CrO₃.
Hydrolysis of Benzonitrile: Acidic (H⁺) or basic (OH⁻) hydrolysis of C₆H₅CN.
Grignard Reagent: Phenylmagnesium bromide (C₆H₅MgBr) with CO₂ followed by hydrolysis.

Properties:

White crystalline solid.
Sparingly soluble in cold water, soluble in hot water and organic solvents.
Weak acid: Stronger than aliphatic carboxylic acids (due to resonance stabilization of carboxylate ion by phenyl group) but weaker than mineral acids.
Sublimes readily.

Reactions:

Salt Formation: Reacts with bases (NaOH, NaHCO₃) to form salts (e.g., Sodium benzoate).
Esterification: Reacts with alcohols in the presence of an acid catalyst (e.g., conc. H₂SO₄) to form esters (e.g., Ethyl benzoate).
Acid Chloride Formation: Reacts with SOCl₂, PCl₅, or PCl₃ to form Benzoyl chloride (C₆H₅COCl).
Reduction: Reduced by LiAlH₄ to Benzyl alcohol (C₆H₅CH₂OH).
Decarboxylation: Heated with soda lime (NaOH + CaO) to yield Benzene.
Electrophilic Substitution: The -COOH group is meta-directing and deactivating.

Nitration: Forms m-Nitrobenzoic acid with conc. HNO₃/H₂SO₄.
Halogenation: Forms m-Bromobenzoic acid with Br₂/FeBr₃.

Salicylic Acid (o-hydroxybenzoic acid):
Structure: Possesses both a phenolic hydroxyl (-OH) group and a carboxylic acid (COOH) group, ortho to each other.
Preparation:

Kolbe's Reaction (Kolbe-Schmitt Reaction): Phenol reacts with sodium hydroxide to form sodium phenoxide, which then reacts with carbon dioxide under pressure (4-7 atm) and moderate temperature (125-140°C), followed by acidification, to yield Salicylic acid.

Properties:

Colorless crystalline solid.
Moderately soluble in water.
Exhibits intramolecular hydrogen bonding (chelation) between ortho OH and -COOH groups.
Weak acid.
Gives a violet color with neutral ferric chloride solution (characteristic of phenolic -OH).

Reactions:

Reactions involving Carboxylic Acid group (-COOH):

Esterification with Methanol/ H⁺: Forms Methyl Salicylate, commonly known as Oil of wintergreen (used as a liniment).

Reactions involving Phenolic Hydroxyl group (-OH):

Acetylation with Acetic Anhydride ((CH₃CO)₂O) or Acetyl Chloride: Forms Acetylsalicylic Acid.

Important Derivatives & Common Names:

Acetylsalicylic Acid: Also known as o-acetoxybenzoic acid, commonly called Aspirin. (Answers MCQ 1 & 2)
Methyl Salicylate: Oil of wintergreen.

Decarboxylation: Heating salicylic acid alone or with soda lime yields Phenol and CO₂.

Definition, Classification, and Nomenclature of Organic Acids

Definition: Organic acids are carbon-containing compounds with acidic properties, primarily due to the presence of an acidic functional group.
The most common organic acids are Carboxylic acids, characterized by the carboxyl functional group (-COOH).
Examples: Acetic acid (CH₃COOH), Citric acid. (Contrast with inorganic acids like Hydrochloric acid, Nitric acid, Sulphuric acid).
Classification:

Based on Functional Group:

Carboxylic Acids (R-COOH): Most prevalent, e.g., Acetic acid, Citric acid.
Sulfonic Acids (R-SO₃H): Organic compounds containing the -SO₃H group.
Sulfenic Acids (R-SOH): Unstable organic acids; released by onions, causing tears.

Based on Number of Carboxyl Groups (Basicity):

Monocarboxylic Acids: One COOH group (e.g., Acetic acid).
Dicarboxylic Acids: Two COOH groups (e.g., Oxalic acid).
Tricarboxylic Acids: Three COOH groups (e.g., Citric acid).

Nomenclature (IUPAC for Carboxylic Acids):

The longest carbon chain containing the -COOH group is the parent chain.
The suffix '-e' of the corresponding alkane name is replaced by '-oic acid'.
The carbon atom of the -COOH group is always assigned position '1'.
Substituents are named and numbered according to their positions on the parent chain.
Example: For Phenyl-CH₂COOH: The parent chain is ethanoic acid (with COOH at C1, -CH₂ at C2). A Phenyl group is attached at C2. Thus, the IUPAC name is 2-phenyl ethanoic acid.

Dicarboxylic Acids: Oxalic Acid, Malonic Acid, Succinic Acid, Adipic Acid

Dicarboxylic Acids are organic compounds 1. characterized by the presence of two carboxyl (-COOH) functional groups. Oxalic Acid: 2.

Structure: HOOCCOOH (Ethane-1,2dioic acid).
Simplest and strongest dicarboxylic acid.
Used in rust removal, as a bleaching agent, and in analysis. Malonic Acid: 3.
Structure: HOOCCH₂COOH (Propane-1,3-dioic acid).
Features one methylene group (-CH₂) between the carboxyl groups.
Key reactant in organic synthesis, particularly in malonic ester synthesis and Knoevenagel condensation. Succinic Acid: 4.
Structure: HOOC(CH₂)₂COOH (Butane-1,4-dioic acid).
Contains two methylene groups (-CH₂) between the carboxyl groups.
An essential intermediate in the Krebs cycle (Tricarboxylic Acid cycle) within cellular respiration.
Utilized as a food additive (acidity regulator) and in the production of certain polymers and pharmaceuticals. Adipic Acid: 5.
Structure: HOOC(CH₂)₄COOH (Hexane-1,6-dioic acid).
Characterized by four methylene groups (-CH₂) between the carboxyl groups.
Predominantly used as a monomer in the production of Nylon 6,6, a highperformance polyamide.
Also finds application in the manufacture of polyurethanes and plasticizers. Tartaric Acid: 6.
A dihydroxy-dicarboxylic acid (2,3-dihydroxybutanedioic acid).
Widely used as an acidulant in the food industry, notably as an active component in baking powder and in various beverages and candies.

Hydroxy Acids (e.g., Lactic Acid, Citric Acid, Tartaric Acid) and Keto Acids (e.g., Pyruvic Acid)

Hydroxy Acids: Organic acids containing both hydroxyl (-OH) and carboxyl (-COOH) functional groups.
Lactic Acid:

Source: Sour milk, curd, milk.
Formation: During the conversion of milk into curd.

Citric Acid:

Source: Lemons, other citrus fruits.
Type: A tricarboxylic hydroxy acid.

Tartaric Acid:

Source: Tamarind, grapes, bananas.
Type: A dicarboxylic hydroxy acid.

Malic Acid:

Source: Apples, pears.
Type: A dicarboxylic hydroxy acid.

Keto Acids: Organic acids containing both a keto (C=O) and a carboxyl (-COOH) functional group.
Pyruvic Acid: A simple alpha-keto acid. (No specific sources or properties covered by MCQs, just its classification).
Other Relevant Organic Acids from MCQs:
Acetic Acid:

Source: Vinegar.

Formic Acid (Methanoic Acid):

Source: Ant stings, stinging hair of nettle leaves.

Oxalic Acid:

Source: Predominantly found in tomatoes.

Ascorbic Acid (Vitamin C):

Source: All citrus fruits.
Key feature: Does NOT contain a COOH (carboxyl) group. Its acidity comes from enol groups in its lactone structure.

Industrial Applications and Biological Significance of Organic Acids

Lactic acid: Found in curd; responsible for souring of milk.
Methanoic acid (Formic acid): Present in ant stings.
Oxalic acid: Present in tomatoes.
Maleic acid: Listed as present in apples (Note: Malic acid is the primary acid in apples).
Acetic acid: Present in vinegar.
Calcium phosphate: Main compound found in bones.
Ethylene: Plant hormone responsible for fruit ripening (Note: not an organic acid).

Reactions of Carboxylic Acids: Formation of Acyl Halides, Anhydrides, and Amides

Formation of Acyl Halides (e.g., Acyl Chlorides):

Carboxylic acids react with thionyl chloride (SOCl₂), phosphorus trichloride (PCl₃), or phosphorus pentachloride (PCl₅).
Reaction: RCOOH + SOCl₂ → RCOCl + SO₂↑ + HCl↑ (preferred due to gaseous byproducts).
Other reagents: RCOOH + PCl₃ → RCOCl + H₃PO₃; RCOOH + PCl₅ → RCOCl + POCl₃ + HCl.

Formation of Anhydrides:

Carboxylic acids undergo intermolecular dehydration to form acid anhydrides.
Reagents: Strong dehydrating agents like phosphorus pentoxide (P₂O₅) or concentrated sulfuric acid (conc. H₂SO₄) are used.
Reaction: 2 RCOOH --(P₂O₅ / conc. H₂SO₄, heat)--> (RCO)₂O + H₂O.
Cyclic anhydrides can be formed by heating dicarboxylic acids if a stable 5- or 6-membered ring can result.

Formation of Amides:

Carboxylic acids react with ammonia (NH₃) or primary/secondary amines to first form ammonium carboxylate salts.
Step 1 (Salt formation): RCOOH + NH₃ → RCOONH₄ (Ammonium carboxylate salt).
Step 2 (Amide formation): The ammonium salt, upon heating, dehydrates to form an amide.
Reaction: RCOONH₄ --(Heat)--> RCONH₂ + H₂O (Primary Amide).
Similarly for primary (R'NH₂) or secondary (R'R''NH) amines, forming Nsubstituted amides.

Specific Monocarboxylic Acids: Formic Acid, Acetic Acid, Butyric Acid (Preparation, Properties, Uses)

Formic Acid (Methanoic Acid - HCOOH)

Chemical Name: Methanoic Acid.
Occurrence:

Naturally found in ant stings (causes burning pain and irritation).
Injected by ants when they bite.
Present in bee stings (causes pain and irritation).
Found in the stinging hairs of nettle leaves, causing burning pain.

Acetic Acid (Ethanoic Acid - CH3COOH)

Chemical Name: Ethanoic Acid.
Common Form: Vinegar.
Vinegar Definition: A dilute solution of acetic acid in water.
Concentration in Vinegar: Typically 5-8% acetic acid in water (can be up to 20%).
Properties:

Has an odour resembling that of vinegar.
Pure, water-free acetic acid is known as Glacial Acetic Acid.

Uses:

Widely used as a food preservative (in the form of vinegar).
Used as a flavouring agent.

Butyric Acid (Butanoic Acid CH3(CH2)2COOH)

Chemical Name: Butanoic Acid.
Occurrence: Found in rancid butter.
Properties: Responsible for the characteristic unpleasant odour of rancid butter.

16. The Explosive Substances

Practice MCQs: Organic Acid

Acidity of Carboxylic Acids: Factors Affecting Acidity (Inductive, Resonance Effects, pKa Values)

Which is the stronger acid than phenol due to the presence of three same electron with drawing groups (i) O-Toluic Acid (ii) Benzoic acid (iii) Salicylic Acid (iv) Picric Acid
Asked in: UPPSC Upper Mains 2010
1. (iii) only
2. (i) only
3. (ii) and (iv) only
4. (iv) only B. Nylon C. Polystyrene D. Bakelite
Show answer
Answer: D. (iv) only B. Nylon C. Polystyrene D. Bakelite
Phenol is a key component in the synthesis of Bakelite, which is a phenol-formaldehyde resin. Bakelite was one of the first synthetic plastics.
Which of the following polymers is used to make electrical switches ?
Asked in: Lower Subordinate Services Examination 2024 · TNPSC CS Prelims 2022
1. Glyptal
2. Polystyrene
3. Bakelite
4. Polypropane
Show answer
Answer: C. Bakelite
Bakelite is a thermosetting polymer known for its electrical insulating properties and heat resistance. These characteristics make it ideal for manufacturing electrical switches, handles for cookware, and other electrical components. Ans: D - Electron-withdrawing groups increase acidity by stabilizing the conjugate base. - Nitro groups are strongly electron-withdrawing. - Picric acid has three nitro groups, making it a very strong acid. - Carboxylic acids are generally stronger acids than phenols.
Which is the strongest acid?
Asked in: TNPSC CS Prelims 2014
1. HCOOH
2. CH₃COOH
3. C₃H₇COOH
4. C₂H₅COOH
Show answer
Answer: A. HCOOH
- Carboxylic acids (R-COOH) donate a proton (H⁺) to form a carboxylate anion (R-COO⁻). - Electron- donating groups (like alkyl groups) attached to the carboxyl group destabilize the negative charge on the carboxylate anion by increasing electron density, thus decreasing acidity. - Electron-withdrawing groups stabilize the negative charge by dispersing it, thus increasing acidity.
Which of the following statements about carboxylic acids is/are correct? 1. Simple aliphatic carboxylic acids are soluble in water. 2. Higher carboxylic acids are practically insoluble in water. 3. The acidity of a carboxylic acid depends on the number of carbon atoms present in the hydrocarbon chain. Select the correct answer using the code given below.
Asked in: UPSC CAPF 2018
1. 1 and 2 only
2. 2 and 3 only
3. 1 only
4. 1, 2 and 3
Show answer
Answer: D. 1, 2 and 3
Simple aliphatic carboxylic acids (e.g., formic acid, acetic acid) are soluble in water because the polar carboxyl group (-COOH) can form hydrogen bonds with water molecules. 2. As the hydrocarbon chain length increases in higher carboxylic acids, the nonpolar hydrophobic part dominates, making them practically insoluble in water. 3. The acidity of a carboxylic acid is related to the stability of its conjugate base (carboxylate ion). Alkyl groups are electron-donating, which destabilizes the negative charge on the carboxylate ion. Therefore, increasing the number of carbon atoms (length of the alkyl chain) generally decreases the acidity of aliphatic carboxylic acids. The hydrocarbon chain's size does influence acidity. 4. Assertion (A): Formic acid is a stronger acid than acetic acid. Reason (R): Formic acid is an organic acid.
Asked in: UPPCS Prelims 1998
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is NOT a correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Show answer
Answer: B. Both A and R are true, but R is NOT a correct explanation of A
Assertion A is true (formic acid is stronger than acetic acid). Reason R is true (formic acid is an organic acid). However, R does not explain A.
The correct order of increasing acidic strength of the following acids is - (1) $CCl_3‐ COOH > CF_3COOH > NO_2-CH_2COOH > NC-CH_2COOH$ (2) $CF_3COOH > CCl_3‐ COOH > NO_2-CH_2COOH > NC-CH_2‐ COOH$ (3) $NC-CH_2COOH > NO_2-CH_2‐ COOH > CF_3COOH > CCl_3COOH$ (4) $NO_2-CH_2COOH > CCl_3COOH > CF_3‐ COOH > NC-CH_2COOH$ (5) Question not attempted
Asked in: Department Recruitment 2024 (Chemist) 2024
1. Option 1
2. Option 2
3. Option 3
4. Option 4
Show answer
Answer: B. Option 2
Acidic strength of carboxylic acids increases with the electron-withdrawing ability of substituents on the carbon atom. Electron-withdrawing groups stabilize the carboxylate anion, increasing acidity. The order of electron-withdrawing strength is generally $CF_3 > CCl_3 > NO_2 > NC$.
pKa value of Acetic Acid is
Asked in: Food Safety Officer 2019
1. 4.76
2. 5.65
3. 3.76
4. 3.67
Show answer
Answer: A. 4.76
The pKa value of Acetic Acid is 4.76.
The order of acidic strength of the following is : Phenol, Benzoic acid, p-Nitrophenol
Asked in: lower devision clerk 2025
1. p-Nitrophenol > Benzoic acid > Phenol
2. Benzoic acid > p-Nitrophenol > Phenol
3. Benzoic acid > Phenol > p-Nitrophenol
4. p-Nitrophenol > Phenol > Benzoic acid
Show answer
Answer: B. Benzoic acid > p-Nitrophenol > Phenol
The acidic strength is determined by the stability of the conjugate base. Benzoic acid is more acidic than phenol due to better resonance stabilization of the benzoate ion. p-Nitrophenol is more acidic than phenol due to the electron-withdrawing effect of the nitro group, but benzoic acid is more acidic than p- nitrophenol.

Aromatic Carboxylic Acids: Benzoic Acid, Salicylic Acid (Preparation, Properties, Reactions)

Acetylsalicylic acid is known as:
Asked in: opsc 2025 2025
1. Oil of wintergreen
2. Aspirin
3. Ibuprofen
4. Paracetamol
Show answer
Answer: B. Aspirin
Acetylsalicylic acid is the chemical name for Aspirin, a widely used medication for pain relief, fever reduction, and anti-inflammatory purposes.
Acetoxy Benzoic Acid is commonly called
Asked in: Group B Exam 2012
1. Antiseptic
2. Antibiotic
3. Aspirin
4. Mordent dye
Show answer
Answer: C. Aspirin
This question tests the knowledge of common chemical names of well-known substances.

Definition, Classification, and Nomenclature of Organic Acids

Which one of the following is an organic acid ?
Asked in: UPSC NDA 1 2019
1. Hydrochloric acid
2. Nitric acid
3. Acetic acid
4. Sulphuric acid
Show answer
Answer: C. Acetic acid
- Hydrochloric acid (HCl) is a strong inorganic acid (mineral acid). - Nitric acid (HNO₃) is a strong inorganic acid (mineral acid). - Acetic acid (CH₃COOH) is a carboxylic acid and a weak organic acid. It is the main component of vinegar. - Sulphuric acid (H₂SO₄) is a strong inorganic acid (mineral acid).
Peeling of onions causes tears as onions release
Asked in: UPPCS Prelims 2015
1. Sulphonic acid
2. Sulfenic acid
3. Amino acid
4. Carbolic acid
Show answer
Answer: B. Sulfenic acid
The release of propanethial S-oxide, a volatile sulfur compound derived from sulfenic acids, is responsible for causing tears when cutting onions.
Which is organic Acid:
Asked in: RPSC RAS Prelims 2010
1. Citric Acid
2. Sulfuric Acid
3. Nitric Acid
4. Sulfuric Acid
Show answer
Answer: A. Citric Acid
Sulfuric Acid (H₂SO₄) and Nitric Acid (HNO₃) are inorganic acids, also known as mineral acids. They do not contain carbon in their basic structure. Citric Acid (C₆H₈O₇) is naturally found in citrus fruits and is a common example of an organic acid.
Give the IUPAC name of the following compound : - CH2COOH -
Asked in: Co operative Supervisor & Environment Supervisor (Group C) Exam 2023
1. 2-phenyl ethanoic acid
2. 1-phenyl ethanoic acid
3. 2-benzyl ethanoic acid
4. 1-benzyl ethanoic acid
Show answer
Answer: A. 2-phenyl ethanoic acid
In IUPAC nomenclature, the longest carbon chain containing the principal functional group is identified. Numbering starts from the carbon of the functional group (carboxyl group in this case). Substituents are named and their positions indicated by numbers.

Dicarboxylic Acids: Oxalic Acid, Malonic Acid, Succinic Acid, Adipic Acid

Which acid is described as HOOCCOOH ?
Asked in: BPSC Prelims Exam 68th
1. Oxalic acid
2. Acetic acid
3. Carbonic acid
4. More than one of the above
Show answer
Answer: A. Oxalic acid
Oxalic acid is the simplest dicarboxylic acid. Acetic acid has the formula CH₃COOH, and Carbonic acid has the formula H₂CO₃.
Which one of the following acids is used in the manufacturing of baking powder ?
Asked in: UPPSC Upper Mains 2012
1. Oxalic acid
2. Lactic acid
3. Tartaric acid
4. Benzoic acid
Show answer
Answer: C. Tartaric acid
Tartaric acid (or its salt, potassium bitartrate) is a common acidic ingredient used in the manufacturing of baking powder to react with sodium bicarbonate and produce carbon dioxide.

Hydroxy Acids (e.g., Lactic Acid, Citric Acid, Tartaric Acid) and Keto Acids (e.g., Pyruvic Acid)

Stinging hair of nettle leaves inject fluid in the human body causing burning pain. The fluid is
Asked in: UPSC CDS 2 2022
1. Methanoic acid
2. Tartaric acid
3. Hydrochloric acid
4. Sulphuric acid
Show answer
Answer: A. Methanoic acid
Nettle stings inject chemicals including methanoic acid (formic acid).
Which one of the following sources contains tartaric acid ?
Asked in: UPSC Geoscientist 2024
1. Lemon juice
2. Orange juice
3. Tamarind paste
4. Vinegar
Show answer
Answer: C. Tamarind paste
Tartaric acid is one of the principal acids found in tamarind, contributing to its characteristic sour taste.
Match List I with List II and choose the correct answer from the given options : List I (Acid) List II (Source) (a) Ascorbic acid (i) Apples and pears (b) Malic acid (ii) Ant stings (c) Formic acid (iii) Tamarind and grapes (d) Tartaric acid (iv) All citrus fruits Codes :
Asked in: HPPSC HPAS Prelims 2021
1. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
2. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
3. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
4. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)
Show answer
Answer: C. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
Ascorbic acid (Vitamin C) is found in citrus fruits. Malic acid is found in apples and pears. Formic acid is found in ant stings. Tartaric acid is found in tamarind and grapes.
Which one of the following acids is predominantly found in tomatoes ?
Asked in: UPSC NDA 1 2021
1. Acetic acid
2. Tartaric acid
3. Oxalic acid
4. Lactic acid
Show answer
Answer: C. Oxalic acid
Oxalic acid is a dicarboxylic acid (COOH-COOH) found in many plants. Acetic acid is the primary component of vinegar. Tartaric acid is found in grapes and tamarind. Lactic acid is produced during fermentation (e.g., in yogurt) and in muscles during strenuous exercise.
Which one of the following organic acids is abundant in grapes, tamarind and banana?
Asked in: UPPCS Prelims 2017
1. Acetic acid
2. Citric acid
3. Lactic acid
4. Tartaric acid
Show answer
Answer: D. Tartaric acid
Tartaric acid is a naturally occurring organic acid found in several fruits, including grapes, tamarind, and bananas.
Which one of the following does NOT contain COOH group ?
Asked in: UPSC CAPF 2019
1. Citric acid
2. Lactic acid
3. Tartaric acid
4. Ascorbic acid
Show answer
Answer: D. Ascorbic acid
The question asks which of the listed compounds does NOT contain a carboxylic acid group (- COOH). Citric acid (C₆H₈O₇) contains three - COOH groups. Lactic acid (C₃H₆O₃) contains one - COOH group and one hydroxyl (-OH) group. Tartaric acid (C₄H₆O₆) contains two -COOH groups and two -OH groups. Ascorbic acid (C₆H₈O₆), also known as Vitamin C, is a weak acid, but its acidity primarily arises from enol groups, not carboxylic acid groups. Its structure is based on a lactone ring and does not contain a -COOH functional group.
Which one of the following acids is present in sour milk products ?
Asked in: UPPSC Upper Mains 2012
1. Acetic Acid
2. Butyric Acid
3. Tartaric Acid
4. Lactic Acid
Show answer
Answer: D. Lactic Acid
Sour milk products like yogurt, curd, kefir, etc., are produced through the fermentation of lactose (the sugar in milk) by lactic acid bacteria. These bacteria convert lactose into lactic acid, which causes the milk to curdle and gives the products their characteristic sour taste.
Which one of the following acid is formed during the change of milk into curd
Asked in: RPSC RAS Prelims 2008
1. Acetic acid
2. Ascorbic Acid
3. Citric Acid
4. Lactic Acid
Show answer
Answer: D. Lactic Acid
The conversion of milk into curd is a process called fermentation, primarily carried out by lactic acid bacteria (like Lactobacillus). These bacteria ferment the lactose (milk sugar) present in milk into lactic acid. The increase in lactic acid concentration causes the proteins in the milk (casein) to coagulate, resulting in the thickened texture of curd.
Which of the following pairs is/are NOT correctly matched ? (Acid) (Acid found in) 1. Lactic acid - Curd 2. Tartaric acid - Grapes 3. Acetic acid - Potato Select the correct answer from the code given below : Code :
Asked in: uppsc 2025 2025
1. 1 and 2
2. 2 and 3
3. Only 3
4. Only 1
Show answer
Answer: C. Only 3
Identify the correct source of the given acids. Lactic acid is found in curd, tartaric acid in grapes, and acetic acid in vinegar. Potatoes are not a primary source of acetic acid.
Which among the following is the chief natural source of Tartaric acid?
Asked in: Asst. Engineer Comb. Comp. Exam 2018
1. Tomato
2. Vinegar
3. Tamarind
4. Orange
Show answer
Answer: C. Tamarind
Tartaric acid is an antioxidant and is a byproduct of winemaking. It is commonly found in fruits, with tamarinds being a particularly rich source among the options provided.
Which acid is found in Milk ?
Asked in: COMBINED STATE AGRICULTURAL SER‐ VICES (PRE.) EXAM 2024
1. Tartaric acid
2. Oxalic acid
3. Lactic acid
4. Sulfonic acid
Show answer
Answer: C. Lactic acid
Lactic acid is the primary acid responsible for the sour taste of milk when it spoils.
Match List-I with List-II and choose the correct answer using the codes given below : List-I (Natural Source) A. Vinegar B. Tamarind C. Sour milk (curd) D. Nettle sting List-II (Acid) i. Methanoic acid ii. Lactic acid iii. Acetic acid iv. Tartaric acid Codes : (a) A-iii, B-iv, C-ii, D-i (b) A-ii, B-iii, C-iv, D-i (c) A-i, B-iii, C-iv, D-ii (d) A-iv, B-i, C-iii, D-ii
Asked in: RO ARO pre 2023
1. A-iii, B-iv, C-ii, D-i
2. A-ii, B-iii, C-iv, D-i
3. A-i, B-iii, C-iv, D-ii
4. A-iv, B-i, C-iii, D-ii
Show answer
Answer: A. A-iii, B-iv, C-ii, D-i
The matching is as follows: A. Vinegar - iii. Acetic acid B. Tamarind - iv. Tartaric acid C. Sour milk (curd) - ii. Lactic acid D. Nettle sting - i. Methanoic acid (also known as formic acid)

Industrial Applications and Biological Significance of Organic Acids

Match List – I with List – II and choose the correct answer using the code given below the lists. List – I (Natural source of acid) A. Curd B. Ant sting C. Tomato D. Apple List – II (Acid) 1. Oxalic acid 2. Lactic acid 3. Methanoic acid 4. Maleic acid Code : (a) A – 2, B – 3, C – 1, D – 4 (b) A – 4, B – 1, C – 2, D – 3 (c) A – 2, B – 4, C – 1, D – 3 (d) A – 2, B – 3, C – 4, D – 1
Asked in: Assistant Town Planner (Pre.) Exam 2023
1. A – 2, B – 3, C – 1, D – 4
2. A – 4, B – 1, C – 2, D – 3
3. A – 2, B – 4, C – 1, D – 3
4. A – 2, B – 3, C – 4, D – 1
Show answer
Answer: A. A – 2, B – 3, C – 1, D – 4
This question tests knowledge of common organic acids and their natural sources.
Match List – I with List – II and select the correct answer using the code given below the lists: List – I A. Compound present in Bones B. Acid present in vinegar C. Souring of milk D. Ripening of fruits List – II 1. Lactic acid 2. Ethylene 3. Acetic acid 4. Calcium phosphate
Asked in: RO ARO pre 2016
1. A B C D 1 2 3 4
2. A B C D 2 1 4 3
3. A B C D 3 4 2 1
4. A B C D 4 3 1 2
Show answer
Answer: D. A B C D 4 3 1 2
Bones are primarily composed of hydroxyapatite, a form of calcium phosphate. Vinegar is an aqueous solution of acetic acid. The souring of milk is due to the conversion of lactose into lactic acid by bacteria. Ethylene is a plant hormone that plays a significant role in the ripening of fruits.

Reactions of Carboxylic Acids: Formation of Acyl Halides, Anhydrides, and Amides

R - C - O - H + H - O - C - R || || O O P$_2$O$_5$ / Conc. H$_2$SO$_4$ $\longrightarrow$ Main Product Main Product is
Asked in: Food Safety Officer 2019
1. Anhydride
2. Ketone
3. Carboxylic Acid
4. Aldehyde
Show answer
Answer: A. Anhydride
The reaction is the dehydration of two carboxylic acid molecules to form a carboxylic anhydride.

Specific Monocarboxylic Acids: Formic Acid, Acetic Acid, Butyric Acid (Preparation, Properties, Uses)

The chemical name for vinegar is
Asked in: BPSC Prelims Exam 63rd
1. methanol
2. ethanol
3. acetic acid
4. ethyl acetate
Show answer
Answer: C. acetic acid
- Vinegar is primarily an aqueous solution of acetic acid. - Chemical formula of acetic acid is CH₃COOH.
The odour of acetic acid resembles that of
Asked in: BPSC Prelims Exam 68th
1. tomato
2. kerosene
3. vinegar
4. More than one of the above
Show answer
Answer: C. vinegar
The common name for a dilute solution of acetic acid is vinegar. Therefore, the odor of acetic acid is synonymous with the odor of vinegar.
Methanoic acid is normally found in :
Asked in: UPSC CDS 1 2022
1. muscles
2. urine
3. ant stings
4. human brain
Show answer
Answer: C. ant stings
Methanoic acid is the simplest carboxylic acid. Its historical name, formic acid, comes from the Latin word "formica," meaning ant, due to its initial isolation from ants.
When ants bite, they inject :
Asked in: HPPSC HPAS Prelims 2013 · UPPCS Prelims 1999
1. Glacial acetic acid
2. Methanol
3. Formic acid
4. Stearic acid
Show answer
Answer: C. Formic acid
Ants inject formic acid when they bite, which causes irritation and pain.
जब एक चींटी काटी है ो वह क्या अन्वर्वेͧश करिी है ?
Asked in: HPPSC HPAS Prelims 2013
1. ग्लेlशियल ऐसीlटिक अÌल
2. lमथेनिॉल
3. फॉlमर्तक अÌल
4. lस्टिएåरक अÌल
Show answer
Answer: C. फॉlमर्तक अÌल
चींlटियों के डंक में फॉlमर्तक अÌल (Formic acid) होता है, lजसे मेथेनिोइक अÌल (Methanoic acid) भी कहा जाता है। जब चींटिी काटिती है, तो यह अÌल त्वचा में प्रवेशि करता है, lजससे जलनि और ददर्त होता है।
Stung by hairs of nettle leaves causes burning pain. This is due to the injection of
Asked in: UPSC NDA 1 2017
1. Acetic acid
2. Methanoic acid
3. Sulphuric acid
4. Hydrochloric acid
Show answer
Answer: B. Methanoic acid
Methanoic acid (formic acid) is responsible for the stinging pain from nettle hairs.
Which one among the following is present in the nettle leaf hairs that causes burning pain ?
Asked in: UPSC NDA 1 2024
1. Methanoic acid
2. Ethanoic acid
3. Benzoic acid
4. Acetic acid
Show answer
Answer: A. Methanoic acid
The stinging hairs (trichomes) of nettle plants contain several irritants, including histamine, acetylcholine, serotonin, and an acid. The primary acid responsible for the burning and stinging sensation is formic acid, also known by its IUPAC name, methanoic acid (HCOOH).
The main constituent of Vinegar is:
Asked in: UPSC NDA 2 2015
1. Acetic acid
2. Ascorbic acid
3. Citric acid
4. Tartaric acid
Show answer
Answer: A. Acetic acid
Vinegar is primarily an aqueous solution of acetic acid. Typically, it contains 5-20% acetic acid by volume. Acetic acid is responsible for vinegar's characteristic sour taste and pungent smell.
Vinegar is also known as
Asked in: UPSC NDA 2 2020
1. ethanoic acid
2. nitric acid
3. sulphuric acid
4. tartaric acid
Show answer
Answer: A. ethanoic acid
- Acetic acid (CH₃COOH) is a weak organic acid. - Culinary vinegar typically contains 5% to 8% acetic acid by volume.
Bee sting leaves an acid which causes pain and irritation. The acid released is
Asked in: UPSC NDA 2 2022
1. tartaric acid
2. citric acid
3. ethanoic acid
4. methanoic acid
Show answer
Answer: D. methanoic acid
Bee sting venom contains several substances, including formic acid, which is also known as methanoic acid (HCOOH). This acid is primarily responsible for the pain and irritation experienced from a bee sting.
Vinegar is a solution of
Asked in: PPSC CS Prelims 2018 · School Lecturer (Sanskrit Edu.) 2018
1. 5 – 20% acetic acid in water
2. 25 – 30% acetic acid in water
3. 50% acetic acid in water
4. 40 – 45% acetic acid in water
Show answer
Answer: A. 5 – 20% acetic acid in water
Vinegar is an aqueous solution of acetic acid. The concentration of acetic acid in vinegar varies, but commonly used vinegar for culinary purposes is typically around 5-8%. However, commercial and industrial vinegar can have higher concentrations. The range 5-20% encompasses the common concentrations found in various types of vinegar.
Chemical name of vinegar is
Asked in: WBPSC CS Prelims 2018
1. Sodium nitrate
2. Dilute acetic acid
3. Chloride of lime
4. Calcium
Show answer
Answer: B. Dilute acetic acid
Vinegar is primarily a dilute aqueous solution of acetic acid (CH₃COOH), usually containing 5–20% acetic acid by volume. It is produced by the fermentation of ethanol by acetic acid bacteria.

Acidity of Carboxylic Acids: Factors Affecting Acidity (Inductive, Resonance Effects, pKa Values)

Aromatic Carboxylic Acids: Benzoic Acid, Salicylic Acid (Preparation, Properties, Reactions)

Definition, Classification, and Nomenclature of Organic Acids

Dicarboxylic Acids: Oxalic Acid, Malonic Acid, Succinic Acid, Adipic Acid

Hydroxy Acids (e.g., Lactic Acid, Citric Acid, Tartaric Acid) and Keto Acids (e.g., Pyruvic Acid)

Industrial Applications and Biological Significance of Organic Acids

Reactions of Carboxylic Acids: Formation of Acyl Halides, Anhydrides, and Amides

Specific Monocarboxylic Acids: Formic Acid, Acetic Acid, Butyric Acid (Preparation, Properties, Uses)

16. The Explosive Substances

Practice MCQs: Organic Acid

Acidity of Carboxylic Acids: Factors Affecting Acidity (Inductive, Resonance Effects, pKa Values)

Aromatic Carboxylic Acids: Benzoic Acid, Salicylic Acid (Preparation, Properties, Reactions)

Definition, Classification, and Nomenclature of Organic Acids

Dicarboxylic Acids: Oxalic Acid, Malonic Acid, Succinic Acid, Adipic Acid

Hydroxy Acids (e.g., Lactic Acid, Citric Acid, Tartaric Acid) and Keto Acids (e.g., Pyruvic Acid)

Industrial Applications and Biological Significance of Organic Acids

Reactions of Carboxylic Acids: Formation of Acyl Halides, Anhydrides, and Amides

Specific Monocarboxylic Acids: Formic Acid, Acetic Acid, Butyric Acid (Preparation, Properties, Uses)

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