Question

In phosphine, how does phosphorus have -3 oxidation state, even though the electronegativity of hydrogen is more than phosphorus in Pauling's table?

Answer 1

The electronegativities of hydrogen and phosphorus are so close that the P-H bond is essentially nonpolar.This indicates that H is slightly more electronegative (2.20 compared to 2.19 for P). Looking at the electronegativities, we conclude that P is in the +3 oxidation state with H in the -1 state.
$P{H}_3$ can be prepared by the reaction of $C{a}_3{P}_2$ with $H_{2}O$, analogous to the reaction of water with calcium carbide, calcium nitride, or calcium oxide. Therefore, the chemistry of $P{H}_3$ suggests that P can be regarded as having negative oxidation state.