Question

Generally metals reacts with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except $Mn$ and $Mg$)?

• A. $H_{2}S{O}_4$
• B. $HCl$
• C. $HN{O}_3$
• D. All of these

Answer 1

The correct option is C $HN{O}_3$

Hint: Nitric acid is a strong oxidizing agent that can oxidise hydrogen gas.

Step 1:

Generally metals reacts with acids to give salt and hydrogen gas. For example:

$K\left(s\right)+H_{2}S{O}_4\left(aq\right)\to K_{2}S{O}_4\left(aq\right)+H_2\left(g\right)$.

$2K\left(s\right)+2HCl\left(aq\right)\to 2KCl\left(aq\right)+H_2\left(g\right)$

Step 2:

The end product of the reaction nitric acid with metals depends on the reactivity of the metal since nitric acid is a strong oxidizing agent that can oxidise hydrogen gas produced to water along with the production of oxides of nitrogen.
For example:
$Mg\left(s\right)+2HN{O}_3\left(aq\right)\to Mg\left(N{O}_3{)}_2\right(aq)+H_2(g)$

$8K\left(s\right)+10HN{O}_3\left(aq\right)\to 8KN{O}_3\left(aq\right)+N_{2}O\left(g\right)+5H_{2}O\left(l\right)$

Step 3:
In the second reaction of metal with nitric acid, no hydrogen gas is produced because the hydrogen gas produced by displacement is oxidised to water.
Final step: So, the correct option is (C) $HN{O}_3$.