The products $X$ and $Y$ which are formed in the following sequence of reactions are respectively:
$\text{Phenol}$ $\xrightarrow{dil \ HNO_3} X$ $\xrightarrow{1. Zn/HCl, \Delta \atop 2.(CH_3CO)_2O (1 \ equiv)} Y$

Assertion : Phenol on oxidation with $KMnO_4$ gives meso-tartaric acid.
Reason : Pure phenol is colourless but turns pink due to oxidation to phenoquinone.

Given below are two statements :
Statement $I$ : Picric acid is $2,4,6$-trinitrotoluene.
Statement $II$ : Phenol-$2,4$-disulphonic acid is treated with conc. $HNO_3$ to get picric acid.
In the light of the above statements,choose the most appropriate answer from the options given below :

The major products of Reimer-Tiemann reaction and Kolbe reaction are respectively:

In Kolbe's reaction,instead of phenol,the phenoxide ion is treated with carbon dioxide. Why?

Which of the following phenols has the largest $pK_a$ value (i.e.,is least acidic)?