When P reacts with caustic soda, the products are PH₃ and NaH₂PO₂. This reaction is an example of

$\stackrel{0}{{\mathrm{P}}_4}+3\mathrm{NaOH}+3{\mathrm{H}}_2\mathrm{O}\to \underset{\begin{array}{c}\text{ Sodium }\\ \text{ hypophosphite }\end{array}}{3{\mathrm{NaH}}_2{\mathrm{PO}}_2}+\stackrel{-3}{{\mathrm{PH}}_3}$
It shows oxidation and reduction (Redox) properties. P in P₄​, is in zero oxidation state. In PH₃​, the oxidation state of P is −3, whereas in NaH₂PO₂​, it is +1.