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. 3,1 and 2
B. 2,6 and 3
C. 3,1 and 3
D. 2,3 and 2

Explanation

(A) Anode: `2OH^(-)rarrH_2O+1/2O_2+2e`,
Cathode : `Cu^(2+) + 2e `rarr` Cu
`[OH^-]` decreases, thus pH decrease i.e.< 7.