Non-metals is part of Chemistry. Below are notes on 10 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Boron: Boranes, Boric acid, Borax, and uses

  • Boron (B) is the only non-metal in Group 13 of the periodic table.
  • It exhibits covalent bonding and acts as a Lewis acid due to its electron-deficient nature (incomplete octet).
  • Boranes: Hydrides of boron (BxHy).
  • Simplest and most important borane is Diborane (B2H6).
  • Boranes are electron-deficient compounds, characterized by 3-center-2-electron bonds (banana bonds).
  • Diborane can be prepared by the reduction of BF3 with LiAlH4 or NaBH4.
  • Boric Acid (Orthoboric acid): Formula H3BO3 or B(OH)3.
  • It is a weak monobasic Lewis acid, accepting a hydroxide ion from water rather than donating a proton: B(OH)3 + H2O ⇌ [B(OH)4]- + H+.
  • Boric acid has a layered structure where H3BO3 units are linked by hydrogen bonds.
  • Uses of Boric Acid: Antiseptic (e.g., eye wash), mild insecticide, flux, fire retardant.
  • Borax: Sodium tetraborate decahydrate (Na2B4O7.10H2O).
  • Its structure contains [B4O5(OH)4]2- units.
  • Borax Bead Test: A qualitative test for identifying colored metal ions; involves forming characteristic colored metal metaborates upon heating with borax.
  • Uses of Borax: Manufacture of boric acid, borosilicate glass, enamels, and glazes; acts as a flux in metallurgy; water softening agent; preservative.
  • General Uses of Boron & Compounds:
  • Elemental Boron: Used in control rods of nuclear reactors due to its neutron-absorbing capability.
  • Boron fibers: High strength-to-weight ratio, used in advanced composites (e.g., aerospace).
  • Boron carbide (B4C): Extremely hard abrasive, used in armor and cutting tools.
  • Boron nitride (BN): Can be a lubricant (hexagonal BN, similar to graphite) or an extremely hard material (cubic BN, similar to diamond).

Carbon and its Allotropes (Diamond, Graphite, Fullerenes, Graphene)

  • Carbon (C): A non-metal, tetravalent, forms extensive compounds due to catenation.
  • Allotropes: Different structural forms of the same element in the same physical state.
  • Diamond: Hardest known natural substance, rigid 3D tetrahedral structure (sp³ hybridization), insulator.
  • Graphite: Softest allotrope, layered hexagonal structure (sp² hybridization), good electrical conductor (delocalized electrons), used as lubricant and in pencil leads.
  • Fullerenes (e.g., C₆₀ Buckminsterfullerene): Cage-like structures, sp² hybridization, discovered by Smalley, Curl, and Kroto.
  • Graphene: Single atomic layer of graphite, 2D material, strongest known material, excellent electrical and thermal conductor.
  • Dry Ice: Solid form of Carbon Dioxide (CO₂).

General characteristics and properties of non-metals

  • Non-metals exist in all three states at room temperature: solids (e.g., Carbon, Sulfur, Phosphorus, Boron, Iodine), liquid (Bromine), and gases (e.g., Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Noble gases like Krypton, Radon).
  • Generally non-lustrous (dull); exceptions include Iodine (shows metallic luster) and Carbon (graphite allotrope is lustrous).
  • Poor conductors of heat and electricity (insulators); exception: Graphite (an allotrope of Carbon) is a good conductor of electricity.
  • Non-malleable and non-ductile; solid nonmetals are brittle.
  • Generally have low melting and boiling points (exceptions: Carbon, Boron, Silicon).
  • Possess low density.
  • Non-metal oxides are generally acidic (react with water to form acids, e.g., CO₂, SO₂) or neutral (e.g., CO, N₂O, NO).
  • Elemental non-metals can be monoatomic (Noble gases), diatomic (e.g., H₂, N₂, O₂, F₂, Cl₂), or polyatomic (e.g., Phosphorus as P₄, Sulfur as S₈).
  • Many non-metals (e.g., Hydrogen, Nitrogen, Oxygen) and non-metal compounds (e.g., Carbon dioxide) are gases at room temperature; most non-metal gases are colorless.
  • Oxygen is the most abundant element on Earth (crust, atmosphere, oceans).
  • Metalloids (e.g., Boron, Silicon, Germanium, Arsenic) exhibit properties of both metals and non-metals and are often used as semiconductors.
  • Aluminium (Al) is a metal and a good electrical conductor, not a semiconductor.
  • Crookes glass, containing cerium oxide, is known to block ultraviolet (UV) rays.

Halogens (Fluorine, Chlorine, Bromine, Iodine): General characteristics, preparation, properties, and uses

  • Halogens are Group 17 elements: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At - radioactive).
  • General electronic configuration: ns²np⁵. They require one electron to achieve a stable octet.
  • Highly electronegative non-metals; Fluorine is the most electronegative element.
  • Exist as diatomic molecules (X₂).
  • Physical states at room temperature (25 °C) and atmospheric pressure:
    • Fluorine (F₂): Pale yellow gas.
    • Chlorine (Cl₂): Greenish-yellow gas.
    • Bromine (Br₂): Reddish-brown liquid. (Only non-metal that is liquid at room temperature)
    • Iodine (I₂): Violet-black solid (sublimes easily).
  • Color deepens and physical state changes from gas to liquid to solid down the group (F to I).
  • Melting and boiling points increase down the group due to increasing van der Waals forces.
  • Density increases down the group.
  • Preparation:
    • Fluorine (F₂): Electrolytic method (Moissan's process) from molten KF/ HF mixture. Cannot be prepared chemically due to extreme reactivity.
    • Chlorine (Cl₂): Deacon's process (oxidation of HCl by O₂/CuCl₂), Electrolytic process (brine electrolysis Castner-Kellner cell), Lab: MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O.
    • Bromine (Br₂): From sea water/brine containing bromides by oxidation with Chlorine (2Br⁻ + Cl₂ → Br₂ + 2Cl⁻).
    • Iodine (I₂): From seaweed (kelp) or from Chilean saltpetre (NaIO₃) by reduction.
  • Chemical Properties:
    • Strong oxidizing agents; oxidizing power decreases down the group (F₂ > Cl₂ > Br₂ > I₂). Fluorine is the strongest oxidizing agent.
    • Reactivity decreases down the group.
    • Displace less reactive halogens from their salt solutions (e.g., Cl₂ + 2KBr → 2KCl + Br₂).
    • React with hydrogen to form hydrogen halides (HX); reactivity with H₂ decreases from F to I.
    • Acidic strength of hydrogen halides increases down the group (HF < HCl < HBr < HI). HF is a weak acid due to strong H-bonding.
    • Reducing power of hydrogen halides increases down the group (HF < HCl < HBr < HI).
  • Uses:
    • Fluorine (F): Preparation of UF₆ (nuclear fuel), CFCs, Freons, Teflon (polytetrafluoroethylene, PTFE), SF₆ (electrical insulator), NaF (rat poison), SnF₂ (toothpaste).
    • Chlorine (Cl): Bleaching agent (paper, textiles), disinfectant for water (chlorination), preparation of HCl, bleaching powder, PVC, DDT, phosgene (COCl₂), tear gas.
    • Bromine (Br): Photography (AgBr), sedatives, dyes, ethylene dibromide (fumigant, anti-knock), flame retardants.
    • Iodine (I): Tincture of iodine (antiseptic, alcohol-water mixture), iodized salt (goitre prevention), photography (AgI), dyes, thyroid hormones (thyroxine).

Hydrogen: Position in the periodic table, isotopes, preparation, properties, and uses

  • Position: Unique in periodic table. Resembles both alkali metals (Group 1, e.g., 1s¹ configuration, forms H⁺ ion) and halogens (Group 17, e.g., non-metallic, forms diatomic molecule). Classified as a non-metal.
  • Isotopes:
    • Protium (¹H): No neutron (most common).
    • Deuterium (²H or D): One neutron (heavy hydrogen).
    • Tritium (³H or T): Two neutrons, radioactive.
  • Preparation:
    • Laboratory: Reaction of granulated zinc with dilute acids (e.g., Zn + 2HCl → ZnCl₂ + H₂).
    • Commercial:
      • Electrolysis of acidified water (2H₂O(l) → 2H₂(g) + O₂(g)).
      • Steam reforming of hydrocarbons/coke (e.g., CH₄(g) + H₂O(g) → CO(g) + 3H₂(g) at high temp.).
      • Water-gas shift reaction (CO(g) + H₂O(g) → CO₂(g) + H₂(g) for increased H₂ yield).
  • Properties:
    • Colourless, odourless, tasteless, nontoxic gas.
    • Lightest element.
    • Highly combustible (burns with a pale blue flame to form water), non-supporter of combustion.
    • Strong reducing agent.
    • Forms a positive ion (H⁺) by losing its single electron.
    • Forms stable covalent compounds (e.g., H₂O, HCl, NH₃).
  • Uses:
    • Manufacture of ammonia (Haber process).
    • Hydrogenation of vegetable oils to make vanaspati ghee.
    • Production of methanol and other chemicals.
    • As a rocket fuel.
    • In atomic hydrogen and oxy-hydrogen torches for cutting and welding.
    • Reducing agent in metallurgy.
    • Fuel cells for electricity generation.

Nitrogen: Occurrence, preparation, properties, and compounds (Ammonia, Nitric Acid, Nitrogen Oxides)

  • Nitrogen (N)
    • Occurrence: 78% by volume of atmosphere (N₂). In combined state as nitrates (NaNO₃, KNO₃), proteins.
    • Preparation:
      • Lab: Heating ammonium nitrite (NH₄NO₂) or barium azide (Ba(N₃)₂).
      • Commercial: Fractional distillation of liquid air (N₂ boils at -196°C).
    • Properties: Colourless, odourless, tasteless, non-toxic gas. Chemically inert at room temp due to strong N≡N triple bond.
    • Uses: Inert atmosphere, liquid nitrogen as refrigerant, manufacture of ammonia, nitric acid.
  • Ammonia (NH₃)
    • Preparation:
      • Lab: Heating ammonium salts with bases (e.g., NH₄Cl + Ca(OH)₂).
      • Commercial (Haber Process): N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Conditions: 200 atm, 700 K, Fe catalyst with Mo promoter.
    • Properties: Colourless gas with pungent smell. Basic nature. Easily liquefiable.
    • Uses: Manufacture of fertilizers (urea, ammonium nitrate), nitric acid, refrigerant.
  • Nitric Acid (HNO₃)
    • Preparation:
      • Lab: Heating potassium/sodium nitrate with concentrated H₂SO₄.
      • Commercial (Ostwald Process): Catalytic oxidation of ammonia (4NH₃ + 5O₂ → 4NO + 6H₂O; 2NO + O₂ → 2NO₂; 3NO₂ + H₂O → 2HNO₃ + NO).
    • Properties: Colourless liquid (pure), turns yellowish due to decomposition. Strong oxidizing agent.
    • Uses: Manufacture of fertilizers, explosives (TNT, nitroglycerin), aqua regia (with HCl).
  • Nitrogen Oxides (NOx)
    • Dinitrogen Oxide (N₂O): "Laughing gas", anaesthetic.
    • Nitric Oxide (NO): Colourless, neutral. Air pollutant.
    • Nitrogen Dioxide (NO₂): Reddish brown gas, pungent. Acidic, major air pollutant, causes acid rain.
    • Other oxides: N₂O₃ (blue solid), N₂O₄ (colourless solid/liquid), N₂O₅ (colourless solid).
  • Ozone (O₃) (Allotrope of Oxygen, relevant for MCQ)
    • Occurrence: Stratosphere (protective layer), ground level (pollutant).
    • Preparation: Silent electric discharge through dry oxygen (3O₂ → 2O₃).
    • Properties: Pale blue gas, fish-like odour. Powerful oxidizing agent. Restores colour of blackened lead paintings (oxidizes black PbS to white PbSO₄).
    • Uses: Disinfectant for water, bleaching agent, oxidizer for rocket fuel.

Noble Gases (Helium, Neon, Argon, Krypton, Xenon, Radon): Occurrence, properties, and chemistry of Xenon compounds

  • Noble gases are Group 18 elements: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn).
  • Occurrence:
    • Present in small amounts in the atmosphere.
    • He: Found in natural gas deposits (up to 7% in some), radioactive decay of heavy elements (alpha particles).
    • Ar: Most abundant noble gas in the atmosphere (approx. 0.93% by volume).
    • Rn: Radioactive decay product of Radium (Ra) and Thorium (Th); occurs naturally in rocks and soil.
  • General Properties:
    • Monoatomic, colorless, odorless, tasteless.
    • Chemically inert due to stable electron configuration (complete octet, except He with duplet).
    • Very low melting and boiling points due to weak London dispersion forces.
    • Practically insoluble in water.
    • Valency is zero.
  • Applications & Specific Facts:
    • Helium (He): Non-flammable lighterthan-air gas for balloons, airships. Used in cryogenics (lowest boiling point of any element), deep-sea diving (He-O2 mixture to prevent bends), MRI superconducting magnets, nuclear reactors as a coolant.
    • Neon (Ne): Used in discharge tubes for advertising displays (neon signs give distinctive red-orange glow), indicator lamps.
    • Argon (Ar): Fills electric incandescent bulbs to prevent filament oxidation and prolong lifespan, provides inert atmosphere for welding (e.g., TIG welding), metallurgy (e.g., steel refining), and growing single crystals.
    • Krypton (Kr): Used in high-performance electric lamps (e.g., airport runway lights, flash lamps), photographic flashbulbs.
    • Xenon (Xe): Used in high-intensity discharge lamps (headlights, projection lamps, flash lamps), powerful bactericidal lamps, and as a general anesthetic.
    • Radon (Rn): Radioactive noble gas. Used in radiation therapy for cancer, naturally occurring health hazard in basements/mines.
  • Chemistry of Xenon Compounds:
    • Xenon was the first noble gas observed to form stable chemical compounds (Neil Bartlett, 1962, XePtF6).
    • Reacts primarily with highly electronegative elements like Fluorine (F) and Oxygen (O) due to its relatively lower ionization energy among noble gases.
    • Fluorides of Xenon:
      • Xenon difluoride (XeF2): Linear structure.
      • Xenon tetrafluoride (XeF4): Square planar structure.
      • Xenon hexafluoride (XeF6): Distorted octahedral structure.
    • Oxides of Xenon:
      • Xenon trioxide (XeO3): Pyramidal structure, highly explosive solid.
      • Xenon tetraoxide (XeO4): Tetrahedral structure.
    • Oxyfluorides of Xenon:
      • Xenon oxytetrafluoride (XeOF4): Square pyramidal structure.
      • Xenon dioxydifluoride (XeO2F2).
    • Xenon compounds are strong oxidizing agents.

Oxygen: Occurrence, preparation, properties, Allotropes (Ozone), and Oxides

  • Oxygen (O): Group 16 non-metal, diatomic (O2).
  • Occurrence: Constitutes ~21% by volume of atmosphere; most abundant element in Earth's crust by mass.
  • Preparation (Laboratory):
    • Thermal decomposition of Potassium Chlorate (KClO3) in presence of Manganese Dioxide (MnO2) catalyst: 2KClO3 → 2KCl + 3O2.
    • Decomposition of Hydrogen Peroxide (H2O2) in presence of MnO2 catalyst: 2H2O2 → 2H2O + O2.
  • Preparation (Industrial):
    • Fractional distillation of liquid air.
    • Electrolysis of water.
  • Properties:
    • Colorless, odorless, tasteless gas.
    • Slightly soluble in water (essential for aquatic life).
    • Supports combustion but is non-combustible.
    • Paramagnetic.
    • Highly reactive, strong oxidizing agent.
    • Unites with many metals to form oxides (e.g., 2Mg + O2 → 2MgO).
    • Reacts with non-metals to form acidic oxides.
  • Allotrope: Ozone (O3):
    • Pale blue gas with pungent smell.
    • Formed from O2 by UV radiation (upper atmosphere) or silent electric discharge.
    • Unstable, decomposes to O2: 2O3 → 3O2 (releases nascent oxygen).
    • Strong oxidizing agent due to nascent oxygen.
    • Uses: Disinfectant for water (kills microorganisms), bleaching agent, sterilizing agent.
    • Nature: Not radioactive.
    • Ozone layer in stratosphere protects Earth from harmful UV radiation.
  • Oxides: Binary compounds formed with oxygen.
    • Basic oxides: Metal oxides, react with acids (e.g., Na2O, CaO).
    • Acidic oxides: Non-metal oxides, react with bases (e.g., CO2, SO2).
    • Amphoteric oxides: React with both acids and bases (e.g., Al2O3, ZnO).
    • Neutral oxides: Do not react with acids or bases (e.g., CO, NO, N2O).

Phosphorus: Allotropes (White, Red, Black), preparation, properties, and compounds (Phosphoric Acid, Phosphine)

  • Phosphorus (Group 15 element) commonly exhibits valencies of 3 and 5.
  • Allotropes of Phosphorus: White, Red, and Black.
  • White Phosphorus (P₄):
    • Waxy, translucent, soft solid.
    • Highly poisonous.
    • Dissolves in carbon disulfide (CS₂).
    • Glows in the dark (chemiluminescence/phosphorescence) due to slow oxidation.
    • Highly reactive, low ignition temperature (ignites spontaneously in air).
    • Stored under water to prevent contact with air.
    • Composed of discrete tetrahedral P₄ molecules.
    • Not used in safety matches due to extreme reactivity and toxicity.
  • Red Phosphorus:
    • Obtained by heating white phosphorus at 573K (300°C) in an inert atmosphere.
    • Hard, brittle, non-poisonous.
    • Insoluble in carbon disulfide (CS₂).
    • Does not glow in the dark.
    • Much less reactive and has a higher ignition temperature than white phosphorus.
    • Polymeric structure.
    • Used in the manufacture of safety matches (on the side of the matchbox and as a component in matchstick tips).
  • Black Phosphorus:
    • Most stable allotrope.
    • Obtained by heating white phosphorus under high pressure.
    • Opaque crystalline solid.
    • Good conductor of electricity.
    • Least reactive.
  • Phosphine (PH₃):
    • Colourless gas with a rotten fish smell.
    • Highly poisonous.
    • Burns spontaneously in air when impure (due to P₂H₄).
    • Weak base.
    • Used in Holme's signals (smoke screens for ships).
  • Phosphoric Acid (H₃PO₄):
    • Colourless, viscous liquid.
    • Tribasic acid.
    • Used in fertilizers, detergents, food additives, and rust removers.

Silicon: Silica, Silicates, Silicones, and uses

  • Silicon (Si): Non-metal, Group 14 element, second most abundant element in Earth's crust (after Oxygen).
  • Silica (Silicon Dioxide, SiO2):
    • Exists in crystalline forms (e.g., Quartz, Cristobalite, Tridymite) and amorphous forms (e.g., Kieselguhr, Sand).
    • Sand (impure silica) is the primary source of silica for the manufacturing of glass.
    • Silica gel is used as a desiccant and catalyst support.
  • Silicates:
    • Compounds containing silicon and oxygen, often with metal cations.
    • Basic building block: SiO4 tetrahedra.
    • Examples: Feldspar, Mica, Talc, Asbestos, Cement.
    • Zeolites: Hydrated aluminosilicates, used as ion exchangers (e.g., water softening), molecular sieves, and catalysts.
  • Silicones:
    • Organosilicon polymers containing R2SiO repeating units.
    • Properties: Hydrophobic (water-repellent), high thermal stability, low chemical reactivity, good electrical insulators.
    • Uses: Sealants, adhesives, lubricants, electrical insulation, water-repellent fabrics, cosmetics, surgical implants.
  • General Uses of Silicon & its Compounds:
    • Pure Silicon: Used in semiconductors (microchips) and solar cells.
    • Ferrosilicon alloy: Used as a deoxidizer in steel manufacturing.
    • Silicon carbide (SiC): Abrasive (carborundum).

7. Carbon and Its Various Forms

Practice MCQs: Non-metals

Boron: Boranes, Boric acid, Borax, and uses

  1. Which of the following is a non metal?

    Asked in: APPSC Draughtman 2008

    1. Gallium
    2. Indium
    3. Aluminum
    4. Boron
    Show answer

    Answer: D. Boron

    Among the given options, Gallium (Ga), Indium (In), and Aluminum (Al) are all metals. Boron (B) is classified as a metalloid, which has properties intermediate between those of metals and nonmetals. However, in many general classifications or in the context of distinguishing from typical metals, Boron is grouped with nonmetals due to its chemical behavior (e.g., forms acidic oxides, covalent compounds). It is the only non-metal or metalloid in the list.

Carbon and its Allotropes (Diamond, Graphite, Fullerenes, Graphene)

  1. Consider the following statements: Radon is the heaviest gas. Astatine is a rarer element on Earth. Graphite is an allotrope of carbon. Which among the above statement(s) is/are correct ?

    Asked in: PPSC CS Prelims 2015

    1. 1 and 2
    2. 1 and 3
    3. Only 3
    4. All of them
    Show answer

    Answer: D. All of them

    Statement 1: Radon (Rn) is an elemental gas (noble gas) with an atomic weight of approximately 222 g/ mol. Among the elemental gases at standard conditions, it is the heaviest. Statement 2: Astatine (At) is a highly radioactive element and is one of the rarest naturally occurring elements on Earth's crust. It is primarily found as a transient product of radioactive decay. Statement 3: Graphite is a well-known and stable allotrope of carbon, characterized by its layered structure.

  2. Dry ice means

    Asked in: WBPSC CS Prelims 2021

    1. Ice at -23°C
    2. Ice at 4°C
    3. Solid SO₂
    4. Solid CO₂
    Show answer

    Answer: D. Solid CO₂

    Dry ice is the common name for solid carbon dioxide (CO₂). At standard atmospheric pressure, it sublimes, meaning it transitions directly from a solid to a gas without passing through a liquid phase.

General characteristics and properties of non-metals

  1. Which one of the following elements is a non- metal but is lustrous ?

    Asked in: UPSC CDS 1 2021

    1. Carbon
    2. Silicon
    3. Germanium
    4. Iodine
    Show answer

    Answer: D. Iodine

    - Metals are typically lustrous, malleable, ductile, and good conductors of heat and electricity. - Non- metals are typically brittle, non-lustrous, and poor conductors (except for graphite). - Iodine exhibits properties characteristic of non-metals (e.g., it forms negative ions, is a poor conductor of electricity in solid form) but stands out for its metallic lustre in solid state.

  2. Which one of the following statements is true when non-metals are dissolved in water ?

    Asked in: UPSC CDS 1 2022

    1. They produce basic oxides.
    2. They produce acidic oxides.
    3. They produce neutral oxides.
    4. They provide hydroxides.
    Show answer

    Answer: B. They produce acidic oxides.

    Oxides are classified as acidic, basic, amphoteric, or neutral. Non-metal oxides generally react with water to form acids, classifying them as acidic oxides. Metal oxides, in contrast, generally react with water to form bases, classifying them as basic oxides.

  3. Which of the following characteristics is common to hydrogen, nitrogen, oxygen and carbon dioxide?

    Asked in: UPSC CDS 2 2018

    1. They are all diatomic.
    2. They are all gases at room temperature.
    3. They are all coloured.
    4. They all have same reactivity.
    Show answer

    Answer: B. They are all gases at room temperature.

    At standard room temperature (around 20-25 °C) and pressure (1 atm), Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂), and Carbon Dioxide (CO₂) all exist in the gaseous state.

  4. Which one among the following elements is polyatomic ?

    Asked in: UPSC NDA 2 2024

    1. Phosphorus
    2. Sulphur
    3. Chlorine
    4. Aluminium
    Show answer

    Answer: B. Sulphur

    An element is considered polyatomic if its stable molecular form consists of more than two atoms of that element bonded together. Sulphur exists in various allotropes, the most common and stable form being the S₈ molecule, which has a ring structure containing eight sulphur atoms. This makes sulphur a polyatomic element.

  5. Which of the following types of glass can cut off ultraviolet rays?

    Asked in: UPPCS Prelims 2021

    1. Soda glass
    2. Pyrex glass
    3. Jena glass
    4. Crookes glass
    Show answer

    Answer: D. Crookes glass

    Crookes glass is a type of glass containing cerium oxide, which provides the property of absorbing ultraviolet rays. It is often used for making lenses, especially for eyeglasses, to protect eyes from UV damage.

  6. Which one is the most abundant of all the elements on Earth?

    Asked in: UPSC CAPF 2023

    1. Silicon
    2. Aluminium
    3. Carbon
    4. Oxygen
    Show answer

    Answer: D. Oxygen

    The elemental composition of the Earth's crust differs from that of the entire Earth. For the Earth's crust, the most abundant elements by weight are: Oxygen (O) > Silicon (Si) > Aluminium (Al) > Iron (Fe) > Calcium (Ca) > Sodium (Na) > Potassium (K) > Magnesium (Mg). If considering the entire Earth, Iron is the most abundant element, followed by Oxygen, Silicon, and Magnesium, as the core is primarily composed of iron and nickel.

  7. Which one of the following non-metals is present in solid state ?

    Asked in: UPSC CISF AC EXE 2017

    1. Bromine
    2. Boron
    3. Krypton
    4. Radon
    Show answer

    Answer: B. Boron

    Non-metals exist in various states at room temperature: solid (e.g., Carbon, Phosphorus, Sulphur, Boron), liquid (Bromine), and gas (e.g., Hydrogen, Oxygen, Nitrogen, noble gases like Krypton, Radon). Among the given options, Bromine is a liquid, while Krypton and Radon are gases. Boron is a non-metal (or metalloid often grouped with non-metals) and exists as a solid under standard conditions.

  8. Which one of the following Non-metal is lustrous?

    Asked in: Asst. Engineer Comb. Comp. Exam 2018

    1. Iodine
    2. Sulphur
    3. Carbon
    4. Nitrogen
    Show answer

    Answer: A. Iodine

    Luster is a property that describes how light reflects off the surface of a material. Metals are typically known for their luster, while most non-metals are dull. Iodine is an exception among non-metals, possessing a metallic luster.

  9. A Scientist discovers a new element that behaves like both metals and non-metals. Based on periodic trends, in which group this element most likely to be found?

    Asked in: Paper I 6

    1. Halogens
    2. Noble gases
    3. Alkali metals
    4. Metalloids
    Show answer

    Answer: D. Metalloids

    Metalloids are elements that have properties of both metals and non-metals. They are located in the periodic table between metals and non-metals.

  10. Which of the following is not a semi-conductor ?

    Asked in: Rakshak 2023

    1. Ge
    2. Si
    3. GaAs
    4. Al
    Show answer

    Answer: D. Al

    Aluminum is a conductor, not a semiconductor.

Halogens (Fluorine, Chlorine, Bromine, Iodine): General characteristics, preparation, properties, and uses

  1. Which of the following pair of elements exist as liquids at atmospheric pressure and 25 °C temperature ?

    Asked in: ACF And Forest Range Officer Gr I Comp. Exam 2018

    1. Bromine and Caesium
    2. Bromine and Mercury
    3. Mercury and Lithium
    4. Mercury and Argon
    Show answer

    Answer: B. Bromine and Mercury

    This question tests the knowledge of the physical states of elements at standard room temperature and pressure (STP) or similar common conditions (25°C and atmospheric pressure).

  2. Which of the following non-metals is a liquid at room temperature ?

    Asked in: Junior Accountant and TRA 2013

    1. Carbon
    2. Sulphur
    3. Bromine
    4. Iodine
    Show answer

    Answer: C. Bromine

    Bromine is a liquid non-metal at room temperature.

Hydrogen: Position in the periodic table, isotopes, preparation, properties, and uses

  1. The only non-metal which forms positive ion is

    Asked in: ae 2025

    1. hydrogen
    2. helium
    3. argon
    4. oxygen
    Show answer

    Answer: A. hydrogen

    This question tests fundamental knowledge of chemistry, specifically the behavior of elements regarding ion formation. It requires understanding the typical properties of metals and non-metals.

Nitrogen: Occurrence, preparation, properties, and compounds (Ammonia, Nitric Acid, Nitrogen Oxides)

  1. A pale blue gas with a fish-like odour restores the color of a blackened lead painting. The gas is also used as rocket fuel. It is :

    Asked in: HPPSC HPAS Prelims 2011

    1. Oxygen
    2. Ammonia
    3. Sulphur dioxide
    4. Ozone
    Show answer

    Answer: D. Ozone

    Ozone is a strong oxidizing agent. Blackened lead paint is typically lead(II) sulfide (PbS), formed by the reaction of lead-based paint with hydrogen sulfide (H₂S) in the air. Ozone oxidizes PbS (black) to lead(II) sulfate (PbSO₄), which is white, thus restoring the color of the painting. Ozone is also used as an oxidizer in some rocket fuels.

Noble Gases (Helium, Neon, Argon, Krypton, Xenon, Radon): Occurrence, properties, and chemistry of Xenon compounds

  1. The gas that filled the electric bulb is

    Asked in: WBPSC CS Prelims 2020

    1. nitrogen
    2. hydrogen
    3. carbon dioxide
    4. oxygen
    Show answer

    Answer: A. nitrogen

    Inert gases are used in incandescent light bulbs to prolong the life of the filament by preventing oxidation and evaporation.

Oxygen: Occurrence, preparation, properties, Allotropes (Ozone), and Oxides

  1. Consider the following assertion and reason and select the correct answer from the code given below: Assertion (A) : Ozone kills mlcroorganism in water. Reason (R) : Ozone is not radioactive . Codes :

    Asked in: UPPSC Upper Mains 2013

    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 the 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 the correct explanation of (A).

    Assertion (A) is true because ozone (O3) is a powerful oxidizing agent used for disinfection of water, effectively killing microorganisms like bacteria and viruses. Reason (R) is true because ozone, an allotrope of oxygen, is not radioactive; radioactivity relates to the instability of atomic nuclei. However, ozone's ability to kill microorganisms stems from its strong oxidizing property, not from its non-radioactivity.

  2. Which of the following gases in air unites with many metals?

    Asked in: APPSC Draughtman 2008

    1. Hydrogen
    2. Oxygen
    3. Helium
    4. Carbon Dioxide
    Show answer

    Answer: B. Oxygen

    Oxygen is a highly reactive gas and is a significant component of air (about 21%). It readily reacts with many metals, causing oxidation (e.g., rusting of iron, tarnishing of copper and silver).

Phosphorus: Allotropes (White, Red, Black), preparation, properties, and compounds (Phosphoric Acid, Phosphine)

  1. The valency of phosphorus is

    Asked in: UPSC CDS 2 2020

    1. 2, 3
    2. 3, 4
    3. 4, 5
    4. 3, 5
    Show answer

    Answer: D. 3, 5

    Phosphorus is in Group 15 (VA). In compounds like PH₃ or PCl₃, phosphorus has a valency of 3, using its three unpaired p-electrons for bonding. Due to the presence of vacant d-orbitals, phosphorus can expand its valence shell and form five covalent bonds, as seen in compounds like PCl₅ or P₂O₅, where its valency is 5.

  2. The phosphorus used in the manufacture of safety matches is

    Asked in: UPSC NDA 1 2016

    1. Red phosphorus
    2. Black phosphorus
    3. White phosphorus
    4. Scarlet phosphorus
    Show answer

    Answer: A. Red phosphorus

    Red phosphorus is used in safety matches due to its relatively low reactivity and non-toxicity compared to white phosphorus.

  3. White Phosphorus glows in the dark due to:

    Asked in: UPSC NDA 2 2015

    1. amorphous character
    2. slow oxidation
    3. high ignition temperature
    4. good conducting property of electricity
    Show answer

    Answer: B. slow oxidation

    White phosphorus exhibits phosphorescence, which is a form of chemiluminescence resulting from its slow oxidation when exposed to air. This process releases energy in the form of light, causing it to glow faintly in the dark. This is often referred to as 'cold light'.

  4. Which one of the following elements is used in the manufacture of safety matches ?

    Asked in: UPPCS Prelims 2008

    1. Graphite
    2. Phosphorus
    3. Silicon
    4. Sodium
    Show answer

    Answer: B. Phosphorus

    Red phosphorus is a key component of the striking surface on the side of a safety matchbox. Friction converts red phosphorus into white phosphorus, which ignites the mixture on the match head containing potassium chlorate and sulfur.

  5. The Matchstic tips are loaded with

    Asked in: District Statistical Officer Assistant Director 2025

    1. White Phosphorus
    2. Red Phosphorus
    3. Phosphorus Trichloride
    4. Phosphorus Pentaoxides
    Show answer

    Answer: B. Red Phosphorus

    The ignitable component on matchstick tips, particularly in safety matches, is related to phosphorus compounds. Red phosphorus is commonly associated with the striking mechanism.

  6. Which one of the following is used for manufacturing safety matches ?

    Asked in: RO ARO pre 2016

    1. Di- phosphorus
    2. Black phosphorus
    3. Red phosphorus
    4. Scarlet phosphorus
    Show answer

    Answer: C. Red phosphorus

    RO ARO pre -2016 The striking surface of a safety matchbox contains red phosphorus and powdered glass. When the matchstick (which has a head containing potassium chlorate and sulfur) is struck against this surface, the friction ignites the red phosphorus, which in turn ignites the match head.