What happens when
$(i)$ $n$-butyl chloride is treated with alcoholic $KOH$.
$(ii)$ bromobenzene is treated with $Mg$ in the presence of dry ether.
$(iii)$ chlorobenzene is subjected to hydrolysis.
$(iv)$ ethyl chloride is treated with aqueous $KOH$.
$(v)$ methyl bromide is treated with sodium in the presence of dry ether.
$(vi)$ methyl chloride is treated with $KCN$?

$(i)$ When $n$-butyl chloride is treated with alcoholic $KOH$,the formation of but-$1$-ene takes place. This reaction is a dehydrohalogenation reaction.
$CH_3-CH_2-CH_2-CH_2-Cl \xrightarrow[Dehydrohalogenation]{KOH(alc)/\Delta} CH_3-CH_2-CH=CH_2 + KCl + H_2O$
$(ii)$ When bromobenzene is treated with $Mg$ in the presence of dry ether,phenylmagnesium bromide is formed.
$C_6H_5Br + Mg \xrightarrow[Dry\ ether]{} C_6H_5MgBr$
$(iii)$ Chlorobenzene does not undergo hydrolysis under normal conditions. However,it undergoes hydrolysis when heated in an aqueous sodium hydroxide solution at a temperature of $623 \ K$ and a pressure of $300 \ atm$ to form phenol.
$C_6H_5Cl \xrightarrow[623 \ K, 300 \ atm]{NaOH(aq)} C_6H_5OH + NaCl$
$(iv)$ When ethyl chloride is treated with aqueous $KOH$,it undergoes hydrolysis to form ethanol.
$CH_3-CH_2-Cl + KOH(aq) \rightarrow CH_3-CH_2-OH + KCl$
$(v)$ When methyl bromide is treated with sodium in the presence of dry ether,ethane is formed. This reaction is known as the Wurtz reaction.
$2CH_3-Br + 2Na \xrightarrow[Dry\ ether]{} CH_3-CH_3 + 2NaBr$
$(vi)$ When methyl chloride is treated with $KCN$,it undergoes a substitution reaction to give methyl cyanide.
$CH_3-Cl + KCN \rightarrow CH_3-CN + KCl$