Question

Assertion: The pair of elements Zr-Hf, Nb-Ta, Mo-W, ..., Pd-Pt, Ag-Au possess almost the same values of atomic radii.

Reason: The occurrence of lanthanoid contraction cancels the expected increase in the atomic radii values from Hf to Hg.

Options

• If both Assertion and Reason are CORRECT and Reason is the CORRECT explanation of the Assertion.

• If both Assertion and Reason are CORRECT but Reason is not the CORRECT explanation of the Assertion.

• If Assertion is CORRECT but Reason is INCORRECT.

• If Assertion is INCORRECT but Reason is CORRECT.

Answer 1

If both Assertion and Reason are CORRECT and Reason is the CORRECT explanation of the Assertion.

Explanation:

The assertion is correct because pairs like Zr-Hf, Nb-Ta, Mo-W, Pd-Pt, Ag-Au have almost identical atomic radii. This is due to lanthanoid contraction, which offsets the expected increase in atomic size from the 4d to 5d series. Hence, the reason correctly explains the assertion.