Multiple choice

Which metal ion represents zero value of CFSE, if it is associated with weak field ligand?

  1. Fe3+

  2. Fe2+

  3. Cr2+

  4. Mn+

  5. Mn3+
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A Correct answer
Explanation

In a weak field ligand, the filling of electrons is in accordance with Hund’s rule. The CFSE is given by the formula  CFSE = value of t2g (n) + value of eg (n) Dq, Fe3+ corresponds to the d5 configuration. Now, CFSE for Fe3+ (d5) = - 4 (3) + 6 (2) = - 12 + 12 = 0 Dq CFSE for Fe2+ (d6) = - 4 (4) + 6 (2) = - 16 + 12 = - 4 Dq CFSE for Cr2+ (d4) = - 4 (3) + 6 (1) = - 12 + 6 = - 6 Dq CFSE for Mn+ (d6) = - 4 (4) + 6 (2) = - 16 + 12 = - 4 Dq CFSE for Mn3+ (d4) = - 4 (3) + 6 (1) = - 12 + 6 = - 6 Dq Hence, the metal ion with zero CFSE is Fe3+ when it is associated with weak field ligand.

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