From principle of atomic conservation of carbon atom,
Mole of $M _2 CO _3 \times 1=$ Mole of $CO _2 \times 1$
$\frac{1 gm }{\text { molar mass of } M _2 CO _3}=0.01 \times 1$
$\text { Molar mass of } M _2 CO _3=100\,gm / mole$
(આપેલ: $\mathrm{NaOH}$ નું મોલર દળ $40 \mathrm{gmol}^{-1}$ છે.)