Assertion (A): The size decreases in the order `O^(2-) gt Mg^(2+) gt Al^(3+)`
Assertion (R): In isoelectronic ions, the size decreases with increase in nuclear charge.

Options

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