AP EAMCET · Chemistry · Structure of Atom

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

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.

Verified Solution

Answer & Solution

Correct Answer

(B) Both (A) and (R) are correct and (R) is correct
explanation of (A).

Step-by-step Solution

Detailed explanation

\(\mathrm{Na}^{+}\)and \(\mathrm{Mg}^{2+}\) are isoelectrionic species having \(10 e^{-}\) each. But \(\mathrm{Mg}^{2+}\) has 12 protons while \(\mathrm{Na}^{+}\)has 11 protons. Hence effective nuclear charge is greater in case of \(\mathrm{Mg}^{2+}\). ionic radius…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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

Step-by-step Solution

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