Which of the following compounds undergoes nucleophilic substitution reaction most easily?

What are $Y$ and $Z$ respectively in the following reaction sequence?
Chlorobenzene $\xrightarrow[Conc. H_2SO_4]{HNO_3}$ $X$ (major product) $\xrightarrow{Y}$ $Z$

"The presence of an electron-withdrawing group $\left( -NO_2 \right)$ at the ortho and para positions in haloarenes increases the reactivity of haloarenes towards nucleophilic substitution reactions." Prove this with an example.

Match the reactants in Column-$I$ with their products in Column-$II$.

Column-$I$ (Reactants)	Column-$II$ (Products)
$(A)$ $p$-Nitrochlorobenzene $\xrightarrow[(ii) H^+]{(i) NaOH, 443 \ K}$	$(i)$ Phenol
$(B)$ Chlorobenzene $\xrightarrow[(ii) H^+]{(i) NaOH, 623 \ K, 300 \ atm}$	$(ii)$ $2,4,6$-Trinitrophenol
$(C)$ $2,4$-Dinitrochlorobenzene $\xrightarrow[(ii) H^+]{(i) NaOH, 368 \ K}$	$(iii)$ $2,4$-Dinitrophenol
$(D)$ $2,4,6$-Trinitrochlorobenzene $\xrightarrow{Warm \ H_2O}$	$(iv)$ $p$-Nitrophenol

Which of the following chlorides is the least reactive towards hydrolysis?

The replacement of $Cl$ in chlorobenzene to form phenol requires drastic conditions,but the chlorine in $2,4-$dinitrochlorobenzene is readily replaced because: