JEE Mains · Chemistry · STD 11 - 3. Classification of elements and periodicity in properties

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

Verified Solution

Answer & Solution

Correct Answer

(D) \((A)\) is false but \((R)\) is true

Step-by-step Solution

Detailed explanation

Ionic radius of \(O ^{2-}\) is more than that of \(Mg ^{2+}\) Both \(O ^{2-}\) and \(Mg ^{2+}\) are isoelectronic with \(10\) electrons

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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