Question

Salts of A (atomic weight$=$7), B (atomic weight $=$ 27) and C (atomic weight $=$ $48$) were electrolyzed under identical conditions using the same quantity 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 of A, B and C respectively are:

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

Answer 1

Answer: (B)

$1,3$ and $2$

According to faraday's law:
$W=ZQ=EQ/96500$
For A:
$2.1=\left(7/x\right)Q/96500$
For B:
$2.7=\left(27/y\right)Q/96500$
For C:
$7.2=\left(48/z\right)Q/96500$
$x:y:z::\left(7/2.1\right):\left(27/2.7\right):\left(48/7.2\right)$

$=3.33:10:6.66$

$=1:3:2$

by solving these equations,
$x=1,y=3,z=2$
Option B is correct.