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The incorrect relationship in the following pairs in relation to ionisation enthalpies is (1) Mn2+ < Mn2+ (2) Mn2+ < Fe2+ (3) Mn+ < Cr+ (4) Fe2+ < Fe3+

1. (1) Mn2+ < Mn2+
2. (2) Mn2+ < Fe2+
3. (3) Mn+ < Cr+
4. (4) Fe2+ < Fe3+

Correct answer: (2) Mn2+ < Fe2+

Solution

The correct option is (2) because manganese (Mn) has a lower ionization enthalpy compared to iron (Fe) due to its higher atomic number and effective nuclear charge, which makes it easier to remove an electron from Mn2+ than from Fe2+.

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