Question

Magnesium on reaction with very dilute ${\text{HN}}{{\text{O}}_{\text{3}}}$ gives:
A. ${\text{NO}}$
B. ${{\text{N}}_{\text{2}}}{\text{O}}$
C. ${{\text{H}}_{\text{2}}}$
D. ${\text{N}}{{\text{O}}_{\text{2}}}$

Answer 1

Hint: When magnesium metal reacts with very dilute nitric acid to produce a highly flammable gas. We must know which of the given gases is flammable.

Complete answer:
- We know that nitric acid $\left( {{\text{HN}}{{\text{O}}_{\text{3}}}} \right)$ is a very strong oxidising agent. It is a strong acid and thus, it dissociates completely. Nitric acid can be concentrated or dilute depending on its concentration.
- Concentrated nitric acid on reaction with metals generally gives metal nitrates. Along with metal nitrates it produces nitrogen dioxide and water.
- Dilute nitric acid on reaction with metals generally gives metal nitrates. Along with metal nitrates it produces highly flammable hydrogen gas.
- We know that magnesium belongs to group 2 of the periodic table. Magnesium is highly reactive in nature.
- When magnesium metal reacts with very dilute nitric acid it gives magnesium nitrate $\left( {{\text{Mg}}{{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)}_{\text{2}}}} \right)$. Along with magnesium nitrate highly flammable hydrogen gas $\left( {{{\text{H}}_{\text{2}}}} \right)$ is also produced.
- The balanced chemical reaction of magnesium metal $\left( {{\text{Mg}}} \right)$ with very dilute nitric acid $\left( {{\text{HN}}{{\text{O}}_{\text{3}}}} \right)$ is as follows:
${\text{Mg}} + 2{\text{HN}}{{\text{O}}_{\text{3}}} \to {\text{Mg}}{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)_{\text{2}}} + {{\text{H}}_{\text{2}}}$
Thus, magnesium on reaction with very dilute ${\text{HN}}{{\text{O}}_{\text{3}}}$ gives ${{\text{H}}_{\text{2}}}$.

Thus, the correct option is (C) ${{\text{H}}_{\text{2}}}$.

Note:
Concentrated nitric acid on reaction with metals generally gives metal nitrates. Along with metal nitrates it produces nitrogen dioxide and water. Magnesium metal on reaction with concentrated nitric acid gives magnesium nitrate. Along with magnesium nitrate it produces nitrogen dioxide and water. The reaction of magnesium metal with concentrated nitric acid is as follows:
${\text{Mg}} + 2{\text{HN}}{{\text{O}}_{\text{3}}} \to {\text{Mg}}{\left( {{\text{N}}{{\text{O}}_{\text{3}}}} \right)_{\text{2}}} + {\text{N}}{{\text{O}}_{\text{2}}} + {{\text{H}}_{\text{2}}}{\text{O}}$
Evaporating the solution gives pure magnesium nitrate.