(a) Why does `PCl_3` fume in moisture ?
(b) Are all the five bonds in `PCl_5` molecule equivalent ? Justify your answer.
( c) How do you account for the reducing behaviour of `H_3 PO_2` on the basic of its structure ?
(d) Give the disproportional reaction of `H_3PO_3`.

Explanation

(a) `PCl_3` hydrolyses in the presence of moisture and gives furms of `HCl`.
`PCl_3 + 2 H_3 O rarr H_3 PO_3 + 3 HCl`.
(b) All `5` bonds are not equivalent.
`PCl_5` has trigonal bipyramidal geometry, the three `P-Cl` bonds in the equatorial plane have same bond length and two `p-Cl` bonds in the axial `P-Cl` bonds are longer than equatorial `P-Cl` bonds.
( c) In `H_3PO_2`, two `H` atoms are bonded directly to `P` atom. hence due to weak `P-H` bonds `H_3PO_2` acts as a reducing agent.
(d) `H_3PO_3` on heating gives `H_3PO_3` and `PH_3`.
`underset (Phospho rous)(H_3PO_3) overset (Delta) rarr underset (Phospho ric aci d) (H_3PO_4) + underset (Phosp hi n e aci d) (PH_3)`.