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Which one of the following elements will not react with dilute HCl to

June 1, 2025 by rawan239

Which one of the following elements will not react with dilute HCl to produce H₂ ?

Hg

Al

Mg

Fe

This question was previously asked in

UPSC NDA-1 – 2016

Download PDF Attempt Online

The correct answer is A) Hg.

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.

The reaction of a reactive metal (M) with dilute HCl is typically represented as: M(s) + nHCl(aq) → MClₙ(aq) + n/2 H₂(g), where ‘n’ is the valency of the metal in the chloride. For example, Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). Metals below hydrogen can react with oxidizing acids (like concentrated nitric acid or hot concentrated sulfuric acid) but produce different products (e.g., oxides of nitrogen or sulfur dioxide) instead of hydrogen gas.

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