Question

The pair, referred to as 'chemical twins' is.
A. Ac, Cf
B. Hf, Ta
C. Tc, Re
D. La, Ac

Answer 1

Hint – In order to get the right elements you need to know that chemical twins are those in which the properties of some elements are the same. It is due to lanthanide contraction. Knowing this will give you the right option.

Complete answer:

Due to the presence of f-electrons, the nuclear is not screened effectively. Thus, the atom radius of elements of the second transition series (i.e., Nb, Mo, Tc, etc.) is similar to that of corresponding third transition series elements (i.e., Ta, W, Re).

Hence, Nb -Ta; Mo-W or Tc-Re are called chemical twins.

So, the correct option is C.

Note – To get this question correct you need to know about chemical twins and should also know the similarity between the given elements. You should always consider the electronic configuration of the elements to check its similarity. The less difference in the electronic configuration the more the elements are the same. Using this you can find chemical twins.