Answer

A-PQ;B-P;C-PQS;D-R

Explanation

`CH_3CH =CH_2` (P,Q) Electrophilic addition reactions, Shows peroxide effect with HBr
`CH_3CH = CHCH_3 ` -P- Electrophilic addition reactions
`CH_3CH_2C=CH` -P,Q,S- Electrophilic addition reactions, Shows peroxide effect with HBr, Red ppt. With `CucI//NH_4OH`
Benzene `(C_6H_6)`-(R) -Electrophilic substitution reactions