A translucent white waxy solid (A) on heating in an inert atomosphere is converted to its allotropic form (B). The solid (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 hydrolyses to compound (E ). Identify compounds (A) to (E ).

Explanation

(i) Since a translucent while waxy solid (A), on heating in an inert atmosphere, is converted into its allotrope (B), therefore, (A) is white or yellow phosphorus while (B) is red phosphorus.
`underset("White phosphorus")(P_(4)(s)) overset("Heat, inert gas") (rarr) underset("Red phosphorus")(P_(4)(s))`
(ii) Since allotrope (A) on boiling with dilute aqueous KOH gives a heghly poisonous gas (C) having rotten fish smell, therefore, it is confirmed that allotrope (A) is while phosphorus and the poisonous gas (C) is phosphine `(PH_(3))`
`underset("White phosphorus (A)")(P_(4) (s)) + 3 KOH (aq) + 3H_(2)O(l) overset("Heat") rarr underset("Pot. hypophosphite")(3KH_(2)PO_(2)(aq))+underset("Phosphine (C)")(PH_(3)(g))`
(iii) Since phosphine (C) reacts with excess of chlorine to form a compound (D) which upon hydrolysis gives compound (E), therefore, (D) must be phosphorus pentachloride `(PCl_(5))` and (E) must be phosphoric acid `(H_(3)PO_(4))`.
`underset("Phosphine (C)")(PH_(3)(g))+underset(("Excess"))(4Cl_(2)(g))rarr underset("Phosphorus pentachloride (D)")(PCl_(5)(s))+ 3HCl(g)`
`underset((D))(PCl_(5)(s))+4H_(2)O(l) rarr underset("Phosphoric acid (E)")(H_(3)PO_(4_(aq))+5 HCl(aq))`
Thus, (A) is white phosphorus, (B) is red phosphorous, (C) is phosphine `(PH_(3))`. (D) is phosphorus pentachloride `(PCl_(5))` and (E) is phosphoric acid `(H_(3)PO_(4))`