A translucent white waxy solid A on heating in an inert atmosphere is converted into its allotropic form B. Allotrope 'A' on reaction with véry dilute agueous KOH liberates a highly poisonous gas C having rotten fish smell. With excess of chlorine C form. D whịch hydrolyses to compound E: Identify 'A' to E.

Explanation

Since a translucent white waxy solid .A. on heating in an inert atmosphere is converted into its aliotropic form .B.. .A. is.white or yellow phosphorus while B is red phosphorus:
.P_+x., hange .P_4~s.
White phosphorus .red precipitate Since allotrope A gives a highlỳ poisonous gas .C. having rotten fish smell. with dilute aq. KOH. .A. is confirmed to be white phosphorus and .C. .is phósphine .PH_2.
.C. reacts with excess of .Cl., to form .D.. which on hydrolysis. gives compound .E..

Phosphorous pentachloride .PCl_tS+4 H_2 O_ut rarr H_3 PO_4aq+.5 HClaq.
A- White. phossphorus
B - Red.phosphorous
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