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MHT CET · Chemistry · d and f Block Elements

The pair, that referred as 'chemical twins' is

  1. A Ac, Cf
  2. B Hf, Ta
  3. C \(\mathrm{Tc}\), \(\mathrm{Re}\)
  4. D \(\mathrm{La}, \mathrm{Ac}\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(\mathrm{Tc}\), \(\mathrm{Re}\)

Step-by-step Solution

Detailed explanation

Due to the presence of \(f\) -electrons, the nucleus is not screened effectively. Thus, the atomic radius of elements of second transition series (ie, Nb, Mo, Tc etc) is similar to that of corresponding third transition series elements (ie, Ta, W, Re). Hence, Nb-Ta; Mo-W or Tc-Re are called chemical twins.
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