Explanation

(a)
Molarity = $\frac{of\ solution\ \times \ 10(in\ litre)}{M}$
where, M = molecular weight of the solute
Molarity = $\frac{40\ \times \ 1.2\ \times \ 10}{M\ \ \times 1000}$ …(i)
Molarity = $\frac{weight\ of\ the\ solute\ /M}{volume\ of\ solution\ (in\ litre)}$ …(ii)
From Eqs. (i)and(ii)
$\ \ \ \ \ \frac{weight\ of\ solute}{M\ \times \ 1000} = \ \frac{40\ \times \ 1.2\ \times \ 10}{M \times \ 1000}$
Weight of solute = 480 g