NTA Abhyas JEE Main2020ChemistrySolutionsPractice
The elements X and Y form compound having molecular formula X Y 2 and X Y 4 (both are non-electrolyses). When dissolved in 20   g benzene, 1   g X Y 2 lowers the freezing point by 2 .3 o C whereas 1   g of X Y 4 lowers the freezing point by 1 .3 o C . Molal depression constant for benzene is 5 .1 . Thus atomic masses of X and Y respectively are
Options
- A42.64, 21.10
- B21.10, 42.64
- C25.59, 42.64
- D42.64, 25.69
Correct answer
C. 25.59, 42.64
Step-by-step solution
Δ T f = K f w M . W × 1000 2.3 = 5.1 × 1 M X Y 2 × 1000 20 M X Y 2 = 110.87 and 1.3 = 5 × 1 M X Y 4 × 1000 20 M X Y 4 = 196.15 Now, let atomic mass of X = a and atomic mass of Y = b Thus, a + 2 b = 110.87 and - a ± 4 b = - 196.15 - 2 b = - 85.28 b = 42.64 and thus a = 25.59