$100\;mL$ of a mixture of $NaOH$ and $Na_2SO_4$ is neutralized by $10\;mL$ of $0.5\;M$ $H_2SO_4$. Hence $NaOH$ in $100\;mL$ solution is

Question

$(a)\;0.2g\qquad(b)\;0.4g\qquad(c)\;0.6g\qquad(d)\;None\;of\;these$