Dilute HCl is a non-oxidizing acid. Metals that are more reactive than hydrogen will react with such acids to displace hydrogen gas (H₂). The reactivity of metals can be determined from the electrochemical series (or reactivity series). Metals above hydrogen in the series are more reactive and will displace hydrogen from dilute acids. Metals below hydrogen will not. The relevant part of the reactivity series is (from more reactive to less reactive): ... Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au ... - Al, Mg, and Fe are all above hydrogen in the series, so they will react with dilute HCl to produce H₂ gas. - Hg (Mercury) is below hydrogen in the series, so it will not react with dilute HCl to produce H₂ gas.