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

What are $A$ $\&$ $B$ in the following reaction?
$m-Br-C_6H_4-Cl$ $\xrightarrow{Mg/THF} A$ $\xrightarrow[(ii) \ aq. NH_4Cl]{(i) \ CH_3CHO} B$

The two reactions involved in the conversion of benzene diazonium chloride to diphenyl are respectively:

What is the product $Z$ in the following reaction sequence?
$C_6H_5N_2Cl$ $\xrightarrow{Cu_2Cl_2/HCl} X$ $\xrightarrow{CH_3Cl/Na, \text{dry ether}} Y$ $\xrightarrow{Cl_2/Fe, \text{dark}} Z$

The decreasing order of reactivity of the given compounds towards nucleophilic substitution with aqueous $NaOH$ is:
$(I)$ $1$-bromo-$3$-nitrobenzene
$(II)$ $1$-bromo-$2,4,6$-trinitrobenzene
$(III)$ $1$-bromo-$4$-nitrobenzene
$(IV)$ $1$-bromo-$2,4$-dinitrobenzene

Product $A$ of the given reaction is