Salts of `A` (atomic weight `7`), `B` (atomic weight `27`) and `C` (atomic weight `48`) were electolysed under idential condition using the same quanity of electricity. It was found that when `2.1 g` of `A` was deposited, the weights of `B` and `C` deposited were `2.7` and `7.2 g`. The valencies `A, B` and `C`respectively:

Options

A. 1 , 2 and 3
B. 1 , 3 and 2
C. 3 , 1 and 2
D. 2 , 3 and 1

Answer

B

Explanation

When small quantity of current is passed through solution of different salts , the amount of substanced deposited are in the ratio of their equivalent masses .
Valency = `("At. Mass")/("Eq. mass") = ("At.mass")/("Mass of the substance")`
`therefore` valency of A `:` valency of B `:` valency of C
`= (7)/(2.1) : (27)/(2.7) : (64)/(9.6)`
= `(1)/(0.3) : (1)/(0.1) : (2)/(0.3)`
`= (1)/(0.3) : (3)/(0.1) : (2)/(0.3)`