Question

At low temperature, say below $(-{11}^{\circ }C)$ nitrogen dioxide exist as a trimer.

• A. True
• B. False

Answer 1

The correct option is B False

At low temperatures like $(-{11}^{\circ }C)$ nitrogen dioxide exist as a dimer, not trimer. This is an observation.
$2N{O}_2\rightleftharpoons N_2{O}_4$
(Brown gas) (Colorless solid)
$N_2{O}_4$ is a diamagnetic, colourless substance. The equilibrium shown above becomes more and more favoured in the forward direction as we lower the temperature. Above $\left({21}^{\circ }C\right)$, $N{O}_2$ is a reddish-brown gas and below $\left({21}^{\circ }C\right)$, $N{O}_2$ is a yellowish-brown liquid. On cooling below $(-9^{\circ }C)$ it dimerizes into the colourless $N_2{O}_4$ in the . For the dimer, in the liquid and gaseous states, the following structure is proposed.

The dimer formation can be attributed to the overlap of the $s{p}^2$ hybrid orbitals containing the “odd” electrons. The consequent N—N bonding molecular orbital exhibits weak bonding character. In fact,
the N—N bond energy is only about 60 kJ.$mo{l}^{-1}$.