What is the correct order of nucleophilicity for an $S_N2$ reaction?

Arrange the leaving group ability of the following groups in decreasing order:
$(I)$ $CH_3-C_6H_4-SO_3^-$,$(II)$ $C_6H_5-SO_3^-$,$(III)$ $N_3^-$,$(IV)$ $Br^-$

In the alkaline hydrolysis of a tertiary alkyl halide by aqueous alkali,if the concentration of the alkali is doubled,then the reaction rate:

The set of compounds in which the reactivity of the halogen atom increases in the order is ..........

Which of the following rules applies in the reaction:
$CH_3CHBrCH_2CH_3 \xrightarrow{alc. KOH}$
$(i)$ $CH_3CH = CHCH_3$ (major product)
$(ii)$ $CH_2 = CHCH_2CH_3$ (minor product)

Which of the following,on heating with aqueous $KOH$,produces acetaldehyde?