Given below are two statements: 

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

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is not true but (R) is true
4. Both (A) and (R) are false.

Hint:  If elements have very similar physical and chemical properties than separation of those elements are difficult
Separation of Zr and Hf is difficult because they belong to the same group of Periodic Table. Since the change in
the ionic radii of Hf and Zr are very small, their chemical properties are similar. Thus Separation of Zr and Hf is difficult
This is due to lanthanoid contraction which causes almost similar radii of both of them. Hence, Assertion and Reason are true but
the reason is not the correct explanation of assertion.