Question

Assertion :$N{O}_2$ gas is pramagnetic at room temperature. On cooling below $0^{o}C$, its molecular weight increases and it loses its paramagnetism. When it is reheated, the behaviour is reversed. Reason: $N{O}_2$ has unpaired electron, hence paramagnetic. On cooling, thee is formation of new N - N bond (in $N_2{O}_4$) using this unpaired electron; hence, paramagnetism is lost and molecular weight increases. $2N{O}_2\rightleftharpoons N_2{O}_4$ Resonance forms are only multiple representation of the same structure.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

$N{O}_2$ has unpaired electron, hence paramagnetic. On cooling, there is formation of new $N-N$ bond (in $N_2{O}_4$) using this unpaired electron; hence, paramagnetism is lost and molecular weight increases.

$2N{O}_2\to N_2{O}_4$

Resonance forms are only multiple representations of the same structure.