Assertion (A) : `Na^+ and Mg^2+` ions are isoelectronic but the ionic radius of `Na^+` is greater than the of `Mg^2+`. Reason (R) : The effective nuclear charge of `Na^+` ion is less than that of `Mg ^2+` ion.

Options

A. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
B. Both (A) and (R) are correct and (R) is correct explanation of (A)
C. (A) is not correct but (R) is correct
D. (A) is correct but (R) is not correct .

Answer

B

Explanation

`:. ` For isoelectronic species :
`r prop (1)/("effective nuclear charge") `
`:. ` Both (A) and (R) are correct and (R) is the correct explanation of (A) .