Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : The ionic radii of $O^{2–}$ and $Mg^{2+}$ are same.
Reason (R) : Both $O^{2–}$ and $Mg^{2+}$ are isoelectronic species.
In the light of the above statements, choose the correct answer from the options given below.

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

Answer 1

Answer: (D)

(A) is false but (R) is true.

Answer 2

Correct order of ionic radii:

$O^{–2} > Mg^{+2}$

This is because among isoelectronic species, the size of anions are greater than the size of cations.

Statement (II) is correct as both $O^{–2}$ and $Mg^{+2}$ are isoelectronic.

Hence, the correct option is (D): (A) is false but (R) is true.