Two elements A and B form compounds having molecular formula `AB_(2)` and `AB_(4)`. When dissolved in 20g of benzene, 1g of `AB_(2)` lowers the fpt by 2.3K whereas 1g of `AB_(4)` lowers it by `1.3K (K_(f)` for `C_(6)H_(6) = 5.1 K m^(-1))` At. Mass of A and B are

Options

A. 27, 45
B. 42, 25
C. 52, 48
D. 48, 52

Answer

A

Explanation

`AB_(2) " " AB_(4)`
`Delta T_(f)=i.K_(f)xx m`
`2.3=5.4xx(1)/((A+2B))1.3=5.4xx(1)/((A+4B))`
`xx(1000)/(20) " " xx(1000)/(20)`
`A+2B=117.4 to (1)A+4B=207.78 to (2)`
`A+4B=207.7 " " A+2B=117.4`
`2B=90.3 " " B=45 " " A = 27`