Which of the following compounds is most reactive towards electrophilic nitration?

The major product of the reaction is:

Which of the following has the most stable enol form?

Which order is correct for the decreasing reactivity to ring monobromination of the following compounds: $C_6H_5CH_3$ $(I)$,$C_6H_5COOH$ $(II)$,$C_6H_6$ $(III)$,and $C_6H_5NO_2$ $(IV)$?

Find the products $(C)$ and $(E)$ in the following reaction sequences:
$n$-propyl bromide $\xrightarrow{Na} (A)$ $\xrightarrow[Al_2O_3/773 \ K]{CrO_3} (B)$ $\xrightarrow[500 \ K]{Cl_2/UV} (C)$
$n$-propyl bromide $\xrightarrow{Na} (A)$ $\xrightarrow[Al_2O_3/773 \ K]{CrO_3} (B)$ $\xrightarrow{CH_3Cl/AlCl_3} (D)$ $\xrightarrow{Cl_2/hv} (E)$

Which catalyst is used in the following reaction?