In the Gattermann reaction, which of the following catalysts is used?

Which of the following shows the fastest rate of hydrolysis?

What will be the major product $A$ in the following reaction?

The reaction of aryl halide with sodium metal in dry ether to give biphenyl is known as

Which among the following statements is true about the reactivity of haloarenes towards nucleophilic substitution reactions?
$1$. Haloarenes are very reactive towards nucleophilic substitution reaction.
$2$. In haloarenes,the $C-X$ bond acquires partial double bond character.
$3$. The $C-X$ bond in haloarenes is longer than the $C-X$ bond in haloalkanes.
$4$. In haloarenes,the phenyl cation formed as a result of self-ionisation is stable.

Aryl halides are extremely less reactive towards nucleophilic substitution. Predict and explain the order of reactivity of the following compounds towards nucleophilic substitution:
$(I)$ $p$-nitrochlorobenzene
$(II)$ $2,4$-dinitrochlorobenzene
$(III)$ $2,4,6$-trinitrochlorobenzene