Among the following elements, most acidic oxide is given by

We know that Acidic oxide is formed by non metals.

And,the order of Non metallic character of given elements is  $\mathrm{N}>\mathrm{P}>\mathrm{Sb}>\mathrm{Al}$.

Therefore,

Nitrogen forms most acidic oxide $\left({\mathrm{N}}_2{\mathrm{O}}_5\right)$

Hence, option(C) is the answer.