Identify the correct statements with reference to the given reaction

${\mathrm{P}}_{4}+3{\mathrm{OH}}^{-}+3{\mathrm{H}}_{2}\mathrm{O}\to {\mathrm{PH}}_{3}+3{\mathrm{H}}_{2}{\mathrm{PO}}_{2}^{-}$

1.   Phosphorus is undergoing reduction only

2.  Phosphorus is undergoing oxidation only

3.  Phosphorus is undergoing oxidation as well as reduction

4.  Hydrogen is undergoing neither oxidation nor reduction

(c, d)
Write the O.N. of each element above its symbol, then
${\stackrel{0}{\mathrm{P}}}_{4}+3\stackrel{-2}{\mathrm{O}}\stackrel{+1}{{\mathrm{H}}^{-}}+3{\stackrel{+1}{\mathrm{H}}}_{2}\stackrel{-2}{\mathrm{O}}\to \stackrel{-3}{\mathrm{P}}{\stackrel{+1}{\mathrm{H}}}_{3}+3{\stackrel{+1}{\mathrm{H}}}_{2}\stackrel{+1}{\mathrm{P}}{\mathrm{O}}_{2}^{-}$
In this reaction, O.N. of P increases from 0 in P4 to +1 in ${\mathrm{H}}_{2}{\mathrm{PO}}_{2}^{-}$ and decreases to -3 in PH3, therefore, P undergoes both oxidation as well as reduction. Thus, options (a) and (b) are wrong and option (c) is correct.
Further, O.N. of H remains +1 in all the compounds, i.e., H neither undergoes oxidation nor reduction. Thus, option (d) is correct.