Question

Assertion: Separation of Zr and Hf is difficult.
Reason: Because Zr and Hf lie in the same group.
a) Both assertion and reason are correct and reason is the correct explanation for assertion.
b) Both assertion and reason are correct but reason is not the correct explanation for assertion.
c) Assertion is correct but reason is incorrect.
d) Both assertion and reason are incorrect.

Answer 1

Hint: Zr and Hf are both d-block elements and both are almost similar in sizes and have the same physical and chemical properties and lie in the same group due to the contraction of the lanthanides. Now with the help of this you can easily answer the given statement accordingly.

Complete answer:
Zr stands for Zirconium and Hf stands for hafnium and both come under the category of d-block elements. They are also known as the transition metals.
Now considering the statement as;-
In case of d-block elements, as we move from top to bottom i.e. from transition series to the second transition series, the atomic size increases due to the addition of the new shells but as we move from second transition series to the third transition series, the size almost remains the same. It is so because the increase in size from second to third transition series due to addition of new shells is neutralized by the intervening lanthanide contraction.
In lanthanide contraction, there is steady decrease in atomic and ionic assizes of the lanthanoid elements with increase in the atomic number.
So, that’s why Zr(40) and Hf(72) are almost similar in size and have similar properties and lie in the same group. These found occur together in natural minerals and are difficult to separate.
 Thus, Separation of Zr and Hf is difficult because of the lanthanide contraction.
So, Both assertion and reason are correct but reason is not the correct explanation for assertion.

Hence, option (b) is correct.

Note:
Always keep in mind that due to the lanthanoid contraction, the covalent nature of the lanthanoid hydroxide increases from left to right and the ionic nature of ;lanthanide ion decreases from left to right and vice-versa.