Which of the following reacts with phenol to give salicylaldehyde after hydrolysis?

The correct order of $pK_{a}$ values for the following compounds is:
$(a)$ Phenol
$(b)$ $p$-Dimethylaminophenol
$(c)$ $p$-Nitrophenol
$(d)$ $p$-Isopropylphenol

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:

Which of the following is a true statement about the reaction shown?

Which of the following is most acidic?

Identify the final product obtained when a mixture of vapours of phenol and hydrogen is passed over nickel catalyst at $433 \ K$.