250 ml of a sodium carbonate solution contains 2.65 grams of ${\mathrm{Na}}_2{\mathrm{CO}}_3.$ If 10 ml of this solution is diluted to one litre, what is the concentration of the resultant solution (mol. wt. of ${\mathrm{Na}}_2{\mathrm{CO}}_3$ = 106)

$\begin{array}{l}\mathrm{Molarity}=\frac{\mathrm{W}\left(\mathrm{g}\right)\times 1000}{\mathrm{molecular}\mathrm{wt}.\times \mathrm{V}\left(\mathrm{ml}.\right)}\\ =\frac{2.65\times 1000}{106\times 250}=0.1\mathrm{M}\\ 10\mathrm{ml}\mathrm{of}\mathrm{this}\mathrm{solution}\mathrm{is}\mathrm{diluted}\mathrm{to}1000\mathrm{ml}\\ \hspace{0.17em}{\mathrm{M}}_1{\mathrm{V}}_1={\mathrm{M}}_2{\mathrm{V}}_2\\ \text{.1\hspace{0.17em}\hspace{0.17em}}\times \text{\hspace{0.17em}\hspace{0.17em}10\hspace{0.17em}=x \hspace{0.17em}x 1000\hspace{0.17em}}\\ \mathrm{x}=\frac{0.1\times 10}{1000}=0.001\mathrm{M}.\end{array}$