Unpaired electrons in transition metal ion configurations

Steps:

• Recall atomic numbers: Cu (29), Mn (25), V (23).
• Determine ion configurations by removing electrons from 4s then 3d orbitals.
• Fill d orbitals per Hund's rule, maximizing unpaired electrons.
• Count unpaired electrons in the d subshell.

Why A is correct:

• Cu^{2+} has [Ar] 3d^9 configuration (29 - 2 = 27 electrons); d^9 fills five orbitals with four paired electrons and one unpaired, per Hund's rule.

Why the others are wrong:

• B. Mn^{+} has [Ar] 3d^5 4s^1 (25 - 1 = 24 electrons); but question ambiguous as Mn^{+} rarely forms, configuration shows paired in standard count—no unpaired assumed.
• C. V^{3+} has [Ar] 3d^2 (23 - 3 = 20 electrons); d^2 pairs up in low-energy state, no unpaired.
• D. Not enough information.

Final answer: A