Question

Salts of A (atomic mass 15), B (atomic mass 27) and C (atomic mass 48) were electrolysed using same amount of charge. It was found that when 4.5 g of A was deposited, the masses of B and C deposited were 2.7 g and 9.6 g. The valencies of A, B and C were respectively

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

Answer 1

Answer: (C)

According to Faraday's second law

$\frac{\text{Mass} \, \text{of} \, \text{A}}{\text{Equivalent} \, \text{mass} \, \text{of} \, \text{A}} \text{=} \frac{\text{Mass} \, \text{of} \, \text{B }}{\text{Equivalent} \, \text{mass} \, \text{of} \, \text{B}} \text{=} \frac{\text{Mass} \, \text{of} \, \text{C}}{\text{Equivalent} \, \text{mass} \, \text{of} \, \text{C}}$

$\frac{4.5}{15 / n_{1}}=\frac{2.7}{27 / n_{2}}=\frac{9.6}{48 / n_{3}}$

$n_{1}:n_{2}:n_{3}$

$0.3:0.1:0.2$

$3:1:2$ .