Suppose elements `X` and `Y` combine to form two compounds `XY_(2)` and `X_(3)Y_(2)` when 0.1 mole of former weigh `10 g` while 0.05 mole of the latter weigh `9g`. What are the atomic weights of `X` and `Y`.

Options

A. 60 & 40
B. 30 & 40
C. 40 & 30
D. 40 & 60

Answer

C

Explanation

Molecular weight of `XY_(2)=(wt)/("molar")=(10)/(0.1)=100`
molecular weight of `X_(3)Y_(2)=(9)/(0.05)=180`
Let a and b be the atomic masses of X and Y respectively.
Then a + 2b = 100
3a + 2b = 180
`:.` a = 40 and b = 30