An optically inactive compound (A) having molecular formula `C_(4)H_(11)H` on treatment with `HNO_(2)` gave an alconot (B) which on heating with conc. `H_(2)SO_(4)` at 440 k gave an alkene ( C) . ( C) on treatment with HBr gave an optically active compound (D ) having molecular formula `C_(4)H_(9)Br` Identify (A) ,(B) ,(C) and (D).