A solution is prepared by adding $2 \mathrm{~g}$ of "$\mathrm{X}$" to 1 mole of water. Mass percent of "$\mathrm{X}$" in the solution is :

First, we need to calculate the mass of 1 mole of water (H₂O). The molecular weight of water is 18 g/mol, so 1 mole of water weighs 18 g. <br/><br/>The total mass of the solution is the mass of "X" plus the mass of water, which is 2 g + 18 g = 20 g. <br/><br/>We can calculate the mass percent of "X" in the solution with the following formula: <br/><br/>$$\text{Mass percent of "X"} = \left(\frac{\text{mass of "X"}}{\text{total mass of solution}}\right) \times 100\%$$ <br/><br/>Substitute the given values into the formula : <br/><br/>$$\text{Mass percent of "X"} = \left(\frac{2 \, \text{g}}{20 \, \text{g}}\right) \times 100\% = 10\%$$ <br/><br/>Therefore, Option B, $10\%$, is the correct answer.