The ${\mathrm{Eu}}^{2+}$ ion is a strong reducing agent in spite of its ground state electronic configuration (outermost) : [Atomic number of $\mathrm{Eu}=63$ ]

• A

  $4{\mathrm{f}}^{6}6{\mathrm{s}}^2$
• Correct answer
  B

  $4{\mathrm{f}}^7$
• C

  $4{\mathrm{f}}^{7}6{\mathrm{s}}^2$
• D

  $4{\mathrm{f}}^6$

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