Which of the following atoms or ions has a single unpaired electron? A) He B) Sr C) Na⁺ D) Al E) Be

Question

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Aluminum (Al) has a single unpaired electron in its outermost orbital, giving it a valence electron configuration of 3s23p1. He (helium) has a full outer shell and no unpaired electrons. Sr (strontium) has a valence electron configuration of 5s2, with all of its electrons paired. Na+⁺ (sodium sulfide) is an ionic compound and does not have unpaired electrons. Be (beryllium) has a valence electron configuration of 2s2, with all of its electrons paired.

Which of the Following Atoms or Ions Has a Single