Assertion `(A):` The mobility of `Na^(o+)` is lower than that of `K^(o+)` ion.
Reason `(R): ` The ionic mobility depends upon the effective radius of the ion.

Options

A. If both `(A)` and `(R)` are correct, and `(R)` is the correct explanation of `(A)`.
B. If both `(A)` and `(R)` are correct, but `(R)` is not the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R)` is incorrect.
D. If `(A)` is incorrect, `(R)` is correct.

Answer

C

Explanation

`(A)` is correct but `(R)` is incorrect.
In aqueous medium, the mobilities of cations depend on`:`
`(i)` Charge density `[(` ionic charge `//` ionic size `)` ratio`]`
` (ii)` Extent of hydration
Decreasing order of mobility of cations of first groups are `:`
`Cs^(o+)gt Rb^(o+), K^(o+)gtNa^(o+)gtLi^(o+)`