Question

3) A translucent white waxy solid A on heating in an inert atmosphere is converted in to its allotropic form (B). Allotrope A on reaction with very dilute aqueous KOH liberates a highly poisonous gas C having rotten fish smell. With excess of chlorine A forms D which hydrolysis to compound E. Identify compounds A to E?

Answer 1

translucent waxy solid is actually white phosphorus  (P4)

P4 on heating gives red phosphorus in inert atmosphere

P4 on reaction with KOH gives phosphine , a poisonous gas

   P4   +  KOH + H2O ⇒   PH3 + KH2PO2

now P4 on excess of chlorine  gives PCl5 which on hydrolysis gives POCl3 and H3PO4

P4 + 10Cl2 ⇒  4PCl5

PCl5 + H2O ⇒ POCl3 + 2HCl
POCl3 + 3H2O ⇒  H3PO4  +  3HCl
 
A :  P4 (white)
B : P4 (red)
C :  PH3
D :  PCl5
E : H3PO4