Which of the following is most acidic?

In the given reaction sequence,identify the final product $B$:
Phenol $\xrightarrow[(2) CO_2]{(1) OH^-} A$ $\xrightarrow[Pyridine]{CH_3COCl} B$

Reaction of phenol with $NaOH$ followed by heating with $CO_{2}$ under high pressure,and subsequent acidification gives compound $X$ as the major product,which can be purified by steam distillation. When reacted with acetic anhydride in the presence of a trace amount of conc. $H_{2}SO_{4}$,compound $X$ produces $Y$ as the major product. Compound $Y$ is $....$

The major product $(B)$ of this reaction is:

Thymol,which is primarily a derivative of phenol,is used in which of the following?

For the given compounds,the correct order of increasing $pK_{a}$ value is: