(A) P4O6; (B) PH3; (C) H3PO4; (D) Cu3P2
The given changes are :
P + 3O2(s) (air) → P4O6 (Garlic odour); P4O6 + 6H2O (hot) → 3H3PO4 + PH3
(B) is PH3 having rotten fish smell and neutral towards litmus
3CuSO4 + 2PH3 → Cu3P2 + 3H2SO4 (Cu3P2 is black substance insoluble in water)