Maximum number of unpaired electrons are present in

• Correct answer
  A

  $\mathrm{Gd}^{3+}$
• B

  $\mathrm{Yb}^{2+}$
• C

  $\mathrm{Tb}^{2+}$
• D

  $\mathrm{Pm}^{3+}$

Hence, the correct answer is option: 'A'.