Which one of the following compounds is most acidic?

Which of the following is the weakest acid?

Which of the following compounds has the least $pK_a$ value?

Compound $'P'$ on nitration with dil. $HNO_{3}$ yields two isomers $(A)$ and $(B).$ These isomers can be separated by steam distillation. Isomers $(A)$ and $(B)$ show the intramolecular and intermolecular hydrogen bonding respectively. Compound $(P)$ on reaction with conc. $HNO_{3}$ yields a yellow compound $'C',$ a strong acid. The number of oxygen atoms present in compound $'C'$ is:

Identify the major products $A$ and $B$ for the reaction sequence given below.

The product $(A)$ is: