6.90 grams of metal carbonate was completely decomposed by 50 ml of 2N HCl.  The equivalent weight of metal is

$\frac{\mathrm{NV}\left(\mathrm{inml}\right)}{1000}=\frac{\mathrm{Wt} \mathrm{of} \mathrm{metalcarbonate}}{\mathrm{eq}.\mathrm{wt}\hspace{0.17em}\mathrm{of} \mathrm{metal}\mathrm{\hspace{0.17em}}\mathrm{carbonate}}$

$\frac{50\times 2}{1000}=\frac{6.90}{\mathrm{eq}.\mathrm{wt}\mathrm{of}\mathrm{metal}\mathrm{carbonate}}$

$\therefore$        eq.wt of metal carbonate  = 6.90 x 10 = 69

Eq.wt of metal  +Eq.wt of carbonate = 69

Eq.wt of metal  + 30 = 69

Eq.wt of metal= 69 – 30 = 39