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

Options

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

Answer

C

Explanation

Suppose valencies of A,B and C are a,b, and c respectively. Then their equivalent weights will be (At. Wt/valance) 7/a,27/b and 48/c. when same quantity of electricity is passed, masses deposited are in the ratio of their equivalent weights, i.e.,
`("Mass of A")/("Eq. wt. of A")=("Mass of B")/("Eq. wt of B")=("Mass of C")/("Eq. wt of C")`
`therefore(2.1)/(7//a)=(2.7)/(27//b)=(7.2)/(48//c)` or 0.3 a=0.1, b=0.15c, or 3a=b=1.5c. thus, if b=1, then `a=(1)/(3)`,
`c=(1)/(1.5)=(2)/(3)`
`therefore`Ratio `a:b:c=(1)/(3):1:(2)/(3)=1:3:2`