10g a metal in a reaction produces 12gm of its oxide. The equivalent weight of the metal is 

The mass of metal is10g and that of metal oxide is 12g.

Hence, the mass of oxygen=12−10=2g

Now Equivalent mass of oxygen=8

$\frac{\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{metal}}{\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{oxygen}}=\frac{\mathrm{mass} \mathrm{of} \mathrm{metal}}{\mathrm{mass} \mathrm{of} \mathrm{oxygen}}$

$\mathrm{Equivalent} \mathrm{mass} \mathrm{of} \mathrm{metal}=\frac{10\mathrm{g}}{2\mathrm{g}}\times \left(8\mathrm{g}\right)=40\mathrm{g}$

Therefore, the equivalent mass of metal is 40g.