Which compound has the highest value of $pK_{a}$?

An organic compound with the molecular formula $C_6H_6O$ dissolves in $NaOH$, gives a characteristic colour with neutral $FeCl_3$ and on treatment with bromine water gives a tri-bromo derivative. Which is that compound among the following?

Which among the following is the strongest $o, p-$directing group?

Identify the product $P$ obtained in the following reaction: $C_6H_5OH + HCHO \xrightarrow{\text{Acid}} P$

Reaction of phenol with dil. $HNO_3$ gives

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