Nitric oxide becomes brown when released in air. Why?

Question

(i) Nitric oxide becomes brown when released in air. Why?

(ii) BiCl₃ is more stable than BiCl₅. Why?

Answer 1

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

2NO + O₂ ⟶ 2NO₂​ 

(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.