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Which of the following statements about transition elements is/are correct?

1. The most stable oxidation state is +3, and this stability falls off across the period.
2. Across the 3d series the atomic radii are nearly the same from Cr to Cu.
3. The stability of the +2 oxidation state increases on moving across the period.
4. Some transition elements such as Ni, Fe and Cr can show a zero oxidation state in certain compounds.

Correct answer: Across the 3d series the atomic radii are nearly the same from Cr to Cu.

Solution

The middle 3d elements (Cr to Cu) have nearly constant atomic radii, and metals such as Ni, Fe and Cr show zero oxidation state in carbonyls; the +2 state generally becomes more stable across the period while +3 is not uniformly the most stable. The clearly correct, unambiguous statement is the near-constant atomic radii from Cr to Cu.

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