# $H_3PO_4$ is a tribasic acid and one of its salts is $NaH_2PO_4$. What volume of $1\; M\; NaOH$ solution should be added to $12\; g$ of $NaH_2PO_4$ to convert it into $Na_3PO_4$ ? $(H = 1, O = 16, Na = 23, P = 31)$
$\begin{array}{1 1} 200\;ml \\ 100 \;ml \\ 300 \;ml \\ 80\;ml \end{array}$