A compound \(P\) on treatment with \(C_2H_5MgBr\) in presence of ether followed by acidic hydrolysis produces a compound \(Q\). \(Q\) on treatment with \(Cl_2/red\;P\) in mild condition produces a compound \(R\). Compound \(Q\) on heating with soda lime produces a hydrocarbon \(S\). Compounds \(P\), \(Q\), \(R\) and \(S\) are respectively