Which of the following is the correct electron configuration for Se2−?

Question

Which of the following is the correct electron configuration for Se²⁻? 

Group of answer choices

-[Ar]4s²4d¹⁰4p⁶

-[Ar]4s²3d¹⁰4p²

-[Ar]4s²3d¹⁰4p⁴

-[Ar]4s²3d¹⁰4p⁶

Answer 1

Looking at the periodic table, we find selenium (Se) is in period 4 and group 16, so we know it is a p-block element (has 4 p valence electrons in shell n=4) and has the 3d filled. This would make the configuration for Se [Ar]4s²3d¹⁰4p⁴ but since we are looking at Se^2-, it would have 2 more electrons making it isoelectronic with Kr and the configuration would be [Ar]4s²3d¹⁰4p⁶ (the last choice in the list)