An organic compound ‘A’ `C_(8)H_(6)` on treatment with dilute `H_(2)SO_(4)` containing mercuric sulphate gives compound ‘B’. This compound ‘B’ can also be obtained from a reaction of benzene with acetyl chloride in presence of anhy `AlCl_(3)`. ‘B’ on treatment with `I_(2)` in aq. KOH gives ‘C’ and a yellow compound ‘D’. Identify A, B, C and D. Give the chemical reactions involved.