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An element has the electronic configuration [Rn] 5f⁷ 6d¹ 7s². What is the group number of this element in the periodic table?

1. 3
2. 4
3. 5
4. 6

Correct answer: 3

Solution

The element with configuration [Rn] 5f⁷ 6d¹ 7s² is Curium (Cm, Z=96). Actinides and lanthanides are formally placed in Group 3 of the periodic table (they are the f-block elements branching from Group 3). The group number for actinides is 3.

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