(a) Bond angle in `PH_4` is higher than that in `PH_3`. Why ?
(b) What is formed when `PH_3` reacts with an acid ?

Explanation

(a) In `PH_3`, the presence of lone pair caused the l.p-b.p repulsions which results in decrease of bond angle where as in `PH_4^(+)` there are no I.p. of electrons and so molecule experience only b.p-b.p repulsions. As Ip-b.p. repulsions are greater than b.p.-b.p. repulsions bond angle in `PH_(4)^(+)` is higher than `PH_(3)`.
(b) With an acid, `PH_3` forms phosphonium salt. For example, with HI, it forms phosphonium iodide
`PH_(3) + HI to underset("Phosphonium iodide")(PH_(4)^(+))^(-)`