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

What is $Z$ in the following sequence of reactions?
$p-chloronitrobenzene$ $\xrightarrow{NaOH, 443 \ K} X$ $\xrightarrow{(i) Sn + HCl (ii) NaNO_2 / HCl, 0-5^{\circ}C} Y$ $\xrightarrow{H_3O^{+}, 10^{\circ}C} Z$

Phenol reacts with $CCl_4$ in the presence of aqueous alkali and forms a product which on hydrolysis gives:

Which of the following is most acidic?

Identify the product in the following reaction: $Phenol \xrightarrow{CrO_3} \text{Product}$

Explain how the $-OH$ group attached to the carbon of the benzene ring activates the benzene ring for electrophilic substitution reactions.