Two elements X and Y combine to form two compounds XY₂ and Y₃X₂. 0.1mol of  XY₂ weighs 10g and 0.05mol of Y₃X₂ weighs 9g. Calculate the atomic masses of X and Y.

X=40, Y=30

The correct answer is option 3. X=40, Y=30

\(\text{Suppose atomic masses of X and Y are x and y respectively.}\)

\(\text{Molar Mass of }XY_2\text{ = }x+2y\)

\(\text{But 0.1mol of }XY_2 weighs \text{ = 10g}\)

∴ \(\text{Molar Mass of }XY_2\text{ = }100\)

∴ \(\text{x + 2y = 100       -------------------- (i)}\)

\(\text{Molar Mass of }X_3Y_2\text{ = }3x+2y\)

\(\text{But 0.05mol of }X_3Y_2 weighs \text{ = 9g}\)

∴ \(\text{Molar Mass of }X_3Y_2\text{ = }\frac{9}{0.05}\text{ = }180g\)

∴ \(\text{3x + 2y = 180       -------------------- (ii)}\)

\(\text{Subtracting equation (i) from equation (ii), we get}\)

\(\text{2x=80       or,     x = 40}\)

 \(\text{Substituting in equation (i), we get }\)

\(\text{40 + 2y = 100       or,     2y = 60       or,     y = 30}\)