c
\(H _{3} PO _{3}+2 NaOH \rightarrow Na _{2} HPO _{3}+2 H _{2} O\)

\(\begin{array}{ll}50\, ml & 1\, M \\ 1\, M & V =?\end{array}\)

\(\Rightarrow \frac{ n _{ NaoH }}{ n _{ H _{3} PO _{3}}}=\frac{2}{1}\)

\(\Rightarrow \frac{1 \times V }{50 \times 1}=\frac{2}{1} \Rightarrow{ V _{ NaOH }=100\, ml }\)

\(H _{3} PO _{2}+2 NaOH \rightarrow NaH _{2} PO _{3}+ H _{2} O\)

\(\begin{array}{lc}100\, ml & 1\, M \\ 2\, M & V =?\end{array}\)

\(\Rightarrow \frac{ n _{ NaoH }}{ n _{ H _{3} PO _{3}}}=\frac{1}{1} \Rightarrow \frac{1 \times V }{2 \times 100}=\frac{1}{1} \Rightarrow V _{ NaOH }=200\, ml\)