The incorrect statement about Y is

$$\begin{gathered} {\mathrm{P}}_4+3\mathrm{NaOH}+3{\mathrm{H}}_2\mathrm{O}\to {\mathrm{PH}}_3\uparrow +3\underset{\mathrm{X}}{\underbrace{{\mathrm{NaH}}_2{\mathrm{PO}}_2}} \\ {\mathrm{NaH}}_2{\mathrm{PO}}_2\stackrel{\mathrm{HCl} \left(\mathrm{aq}\right)}{\to }\mathrm{NaCl}+\underset{\mathrm{Y}}{\underbrace{{\mathrm{H}}_3{\mathrm{PO}}_2}} \end{gathered}$$

Y is phosphinic acid, it is a reducing agent because of the presence of two P-H bonds. It is a monobasic acid as it has only one P-OH bond and the oxidation state of P in phosphinic acid is +1.