Kolbe electrolysis of potassium succinate gives ${\mathrm{CO}}_2$ and

The order of decreasing reactivity towards an electrophilic reagent, for the following
(A) Benzene
(B) Toluene
(C) Chlorobenzene and
(D) Phenol

would be

In the sulphonation of benzene, the active electrophilic species is:

Which one of the following alkenes will react faster with ${\mathrm{H}}_2$ under catalytic hydrogenation conditions?

($\mathrm{R}=$ Alkyl substituent)