The number of $\sigma$ bonds in carbolic acid is

When phenol is treated with $D_{2}SO_{4} / D_{2}O$, some of the hydrogens get exchanged. The final product in this exchange reaction is

Given below are two statements:
Statement $I$: The acidic strength of monosubstituted nitrophenol is higher than phenol because of the electron-withdrawing nitro group.
Statement $II$: $o$-nitrophenol,$m$-nitrophenol,and $p$-nitrophenol will have the same acidic strength as they have one nitro group attached to the phenolic ring.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which one of the following compounds is most acidic?

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

Which of the following is $NOT$ a dihydric alcohol?