When compound (A) is treated with conc. `H_(2)SO_(4)`, a reddish brown colour gas (B) is evolved. To this solution, a solution of (C ) is added slowly from the side of the test tube, a blue ring is obtained at the junction of two layers due to formation of (D).
Compound (D) has formula :
A. `C_(6)H_(5)NH-C_(6)H_(5)`
B. `(C_(6)H_(5))_(2)N-N(C_(6)H_(5))_(2)`
C. `C_(6)H_(5)-NH-NH-C_(6)H_(5)`
D.