Nitric oxide becomes brown when released in air. Why?

(i) Nitric oxide becomes brown when released in air. Why?
(ii) $BiC{{l}{3}}$ is more stable than
$BiC{{l}
{5}}$.Why?

(i) Nitric oxide combines with oxygen when exposed to air to give nitrogen dioxide which is brown in colour.

(ii) Bi has little tendency to form pentahalides because + 5 oxidation state of Bi is much less stable than + 3 oxidation state due to inert pair effect.