$40\%$ by weight solution will contain how much mass of the solute in 1 L solution, density of the solution is $1.2 g/mL$

Molarity $=$

$\frac{\% by weight of solute X density of solution X 10 (in litre}{M}$

when $M=\mathrm{mol}.$ weight of the solute

Molarity $=\frac{40\times 1.2\times 10}{M\times 1000}$                   ….(i)

Molarity$=\frac{\text{ weight of the solute/ }M}{\text{ volume of solution (in litre) }}$  …(ii)

From Eqs. (i) and (ii)

$\frac{Weight of solute}{M x 1000}=\frac{40\times 1.2\times 10}{M\times 1000}$

Weight of solute $=480 g.$