Question

Which of the following metals liberate hydrogen with 5% HNO3 ?

(i) Cu
(ii) Zn
(iii) Mn
(iv) Mg  ​

Answer 1

Metals react with nitric acid to produce metal nitrates.

But hydrogen gas is not evolved. This is because nitric acid is a very strong oxidizing agent and as soon as the hydrogen is released it reacts with it to form water. In this process, the nitric acid itself gets reduced.

But Mn and Mg are the only two metals that react with nitric acid to give hydrogen gas.

Mg + 2 HNO₃ → Mg(NO₃)₂ + H₂↑

Mn + 2 HNO₃ → Mn(NO₃)₂ + H₂↑

Answer 2

• From the question, the correct option is both iii and  iv.

• As we know that when metals react with nitric acid they form metal nitrates.

• Nitric acid is a very strong oxidizing agent.

• Mn and Mg metals react with nitric acid to give hydrogen gas.

• $Mg + 2 HNO$3→ $Mg$($NO$₃)₂ $+ H$2↑

• $Mn +$2 $HNO$₃ → $Mn$($NO$₃)₂ + $H$₂↑
• Hence, Mn and Mg metals liberate hydrogen with 5% HNO3.