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

Assertion (A) While going from left to right of the periodic table, the atomic size decreases more rapidly for the \(3 d\)-series compared to the \(4 f\)-series of elements. Reason (R) \(3 d\)-electrons experience lesser shielding than \(4 f\)-electrons. The correct answer is

A Both \((\mathrm{A})\) and \((\mathrm{R})\) are correct and \((\mathrm{R})\) is the correct explanation of (A)
B Both \((A)\) and \((R)\) are correct, but \((R)\) is not the correct explanation of \((\mathrm{A})\)
C (A) is correct but (R) is not correct
D \((A)\) is not correct but (R) is correct

Verified Solution

Answer & Solution

Correct Answer

(A) Both \((\mathrm{A})\) and \((\mathrm{R})\) are correct and \((\mathrm{R})\) is the correct explanation of (A)

Step-by-step Solution

Detailed explanation

While going from left to right of the periodic table, the atomic size decreases more rapidly for the \(3 d\)-series compared to \(4 f\)-series of elements. Also, \(3 d\)-electrons experience lesser shielding than \(4 f\)-electrons. Thus, both Assertion (A) and Reason (R) are…

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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