A translucent white waxy solid (A) on heating in an inert atmosphere is converted 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 forms (D) which hydrolyses to compound (E). Identify compounds (A) to (E).

Explanation

`(A) underset ("Inert atmosphere") overset (Heat) rarr (B)`
`(A) and (B)` allotropes.
`(A) + KOH rarr underset ("Poisonous gas will rotten smell")((C))`
`(C) + Cl_2("Express") rarr (D) overset("Hydrolysis")rarr (E)`
Since `(A)` on heating converts into `(B), (A)` is white phosphorous and `(B)` is red phosphorous.
`underset ("White") (P_4) rarr underset ("Red") (P_4)`
`underset ("White") (P_4) + 3 KOH + 3 H_2 overset (Delta) rarr underset("Potassium hypophosp hite")(3 KH_2 PO_2) + underset ("Phosphine")(PH_3)`
Phosphine `( C)` is highly poisonous gas.
`PH_3 + 4 Cl_2 rarr underset ((D)) (PCl_5) + 3 HCl`
`(D)` is phosphorous pentachloride.
`PCl_5 + 4H_2 O rarr underset (( E)) (H_3 PO_4) + 5 HCl`
`(E)` is phosphorous acid.
Hence `(A)` is white phosphorous, `(B)` is red phosphours, `( C)`is phosphine, `(D)` is phosphorous pentachloride, `(E)` is phosphoric acid.