Elements X and Y form two non-volatile compounds \(\left(\mathrm{XY}\right.\) and \(\left.\mathrm{XY}_3\right)\). When 10 g of XY is dissolved in 50 g of ethanol, the depression in freezing point \(\left(\Delta \mathrm{T}_{\mathrm{f}}\right)\) was 5.333 K. When 10 g of \(\mathrm{XY}_3\) is dissolved in 50 g of ethanol, the was \(\left(\Delta \mathrm{T}_{\mathrm{f}}\right) 2.2857\) K. What are the atomic weights of X and Y respectively? \(\left(\mathrm{K}_{\mathrm{f}}=2 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)\)

1. A \(50 \mathrm{u}, 50 \mathrm{u}\)
2. B \(25 \mathrm{u}, 25 \mathrm{u}\)
3. C \(75 \mathrm{u}, 100 \mathrm{u}\)
4. D \(25 \mathrm{u}, 50 \mathrm{u}\)