Give reasons for the following :
(i) NO (Nitric oxide) is paramagnetic in the gaseous state but diamagnetic in the liquid and solid states. Why?
(ii) Nitric oxide becomes brown when released in air.

Explanation

(i) NO has an odd number of electrons (7 + 8 = 15 electrons) and hence is paramagnetic in the gaseous state. But in liquid and solid states, it exists as a dimer and hence is diamagnetic in these states.
(ii) Nitric oxide has one unpaired electron and hence is very reactive.
As a result, it readily combines with `O_(2)` of the air to form nitrogen dioxide `(NO_(2))` which has brown colour.
`underset(("Colourless"))(2NO) + O_(2) rarr underset(("Brown"))(2NO_(2))`