MHTCET 25 Apr 2025 Shift 2 Paper

Concept:The elevation in boiling point is a colligative property.It depends only on the number of solute particles, not their identity.The mathematical relation is $\Delta T_{b} = K_{b} \times m$.Explanation:We are given the molal elevation constant and the elevation in boiling point.Here, $\Delta T_{b} = 0.8 \mathrm{~K}$ and $K_{b} = 2 \mathrm{~kg} \mathrm{~K} \mathrm{~mol}^{-1}$.The mass of the solvent is given as $0.5 \mathrm{~kg}$.First, calculate the molality of the solution using the formula.$m = \frac{\Delta T_{b}}{K_{b}} = \frac{0.8 \mathrm{~K}}{2 \mathrm{~kg} \mathrm{~K} \mathrm{~mol}^{-1}} = 0.4 \mathrm{~mol} \mathrm{~kg}^{-1}$.Molality is defined as the moles of solute per kilogram of solvent.$m = \frac{n}{W_{kg}}$, where $W_{kg}$ is the mass of the solvent in kilograms.Rearrange the equation to solve for the number of moles $n$.$n = m \times W_{kg}$.Substitute the known values into the equation.$n = 0.4 \mathrm{~mol} \mathrm{~kg}^{-1} \times 0.5 \mathrm{~kg}$.$n = 0.2 \mathrm{~mol}$.Answer:The number of moles of nonvolatile solute dissolved in the solvent is $0.2 \mathrm{~mol}$.Therefore, the correct option is B.