TS EAMCET · Chemistry · Classification of Elements and Periodicity in Properties

Identify the correct order of ionic radii of the following ions.

A \(\mathrm{Al}^{3+}>\mathrm{K}^{+}>\mathrm{Mg}^{2+}>\mathrm{Li}^{+}\)
B \(\mathrm{K}^{+}>\mathrm{Mg}^{2+}>\mathrm{Al}^{3+}>\mathrm{Li}^{+}\)
C \(\mathrm{K}^{+}>\mathrm{Li}^{+}>\mathrm{Mg}^{2+}>\mathrm{Al}^{3+}\)
D \(\mathrm{K}^{+}>\mathrm{Mg}^{2+}>\mathrm{Li}^{+}>\mathrm{Al}^{3+}\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(\mathrm{K}^{+}>\mathrm{Li}^{+}>\mathrm{Mg}^{2+}>\mathrm{Al}^{3+}\)

Step-by-step Solution

Detailed explanation

Ionic radii of alkali metal ion is larger than alkaline earth metals due to higher nuclear charge. On the other hand, on moving down the group ionic radii increases. Thus, correct order of ionic radii is \[ \mathrm{K}^{+}>\mathrm{Li}^{+}>\mathrm{Mg}^{2+}>\mathrm{Al}^{3+} \]

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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