Question

Assertion (A): Separation of Zr and Hf is difficult. Reason (R): Because Zr and Hf lie in the same group of the periodic table.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Separation of \(Zr\) and \(Hf\) is difficult mainly due to lanthanoid contraction.

Answer 1

The Correct Option is B

Concept:
Zirconium \((Zr)\) and Hafnium \((Hf)\) are transition elements. They have very similar chemical properties. Their separation is difficult mainly because of lanthanoid contraction. Due to lanthanoid contraction, the atomic and ionic radii of \(Zr\) and \(Hf\) become almost similar.

Step 1: Check the Assertion.
The assertion says that separation of \(Zr\) and \(Hf\) is difficult. This is true. They show very similar chemical behaviour.

Step 2: Check the Reason.
The reason says that \(Zr\) and \(Hf\) lie in the same group of the periodic table. This is also true. Both belong to group 4.

Step 3: Check whether Reason explains Assertion.
The main reason for difficult separation is not simply that they are in the same group. The stronger and more precise reason is lanthanoid contraction, which makes their radii nearly equal. Therefore, both Assertion and Reason are true, but Reason is not the correct explanation. Hence: \[ \boxed{\text{(B)}} \]