UPSC NDA I 2021 General Ability Solved Paper

Concept:Syngas is a mixture of carbon monoxide ($\mathrm{CO}$) and dihydrogen ($\mathrm{H}_2$), not nitrogen dioxide ($\mathrm{NO}_2$) and $\mathrm{H}_2$.Explanation:Option A is correct: $\mathrm{H}_2$ is lighter than air and insoluble in water.Option B is correct: The high $\mathrm{H-H}$ bond dissociation enthalpy makes $\mathrm{H}_2$ inert at room temperature.Option C is correct: $\mathrm{H}_2$ reacts with alkali metals ($\mathrm{M}$) at high temperature to yield metal hydrides: $\mathrm{H}_2(g) + 2\mathrm{M}(g) \rightarrow 2\mathrm{MH}(s)$.Option D is incorrect: The mixture known as syngas (synthesis gas) is $\mathrm{CO} + \mathrm{H}_2$, not $\mathrm{NO}_2 + \mathrm{H}_2$. For example, $\mathrm{2NO}_2 + 4\mathrm{H}_2$ would produce $\mathrm{N}_2$ and $\mathrm{H}_2\mathrm{O}$, not syngas.Answer:Option D