Consider the following reactions :
$$ \begin{aligned} & \mathrm{PCl}_3+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{~A}+\mathrm{HCl} \\ & \mathrm{~A}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{~B}+\mathrm{HCl} \end{aligned} $$ number of ionisable protons present in the product $B$ $\_\_\_\_$ .