Which following oxides is acidic and has a pungent odour? 

Nitrogen dioxide 

The correct answer is option 4. Nitrogen dioxide.

Nitrogen dioxide is a reddish-brown gas with a pungent, acrid odor and one of the several oxides of nitrogen. When nitrogen dioxide levels are high, the airways get inflamed. Nitrogen dioxide also regarded as a primary and secondary contaminant. As an acidic gas, nitrogen dioxide creates an acidic solution in water.