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Which of the following does NOT correctly represent the order of the property written against it?

1. V2+ < Cr2+ < Mn2+ < Fe2+: paramagnetic behaviour
2. Ni2+ < Co2+ < Fe2+ < Mn2+: ionic size
3. Co3+ < Fe3+ < Cr3+ < Sc3+: stability in aqueous solution
4. Sc < Ti < Cr < Mn: number of oxidation states

Correct answer: V2+ < Cr2+ < Mn2+ < Fe2+: paramagnetic behaviour

Solution

Unpaired electrons: V2+ (d3)=3, Cr2+ (d4)=4, Mn2+ (d5)=5, Fe2+ (d6)=4. So Mn2+ is the most paramagnetic and Fe2+ should be lower than Mn2+; the stated increasing order ending at Fe2+ is wrong.

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