Q32 / 150 · MHT CET 2026 (15 April Shift 2) · Chemistry
Which of the following elements has completely filled 4 f orbital at the expected ground state configuration?
- A$\text{La}$
- Correct answerB$\text{Yb}$
- C$\text{Eu}$
- D$\text{Gd}$
Solution
The electronic configurations of the given elements in their ground state are:
$\text{La} (Z=57) : [\text{Xe}] 5d^{1} 6s^{2}$
$\text{Yb} (Z=70) : [\text{Xe}] 4f^{14} 6s^{2}$
$\text{Eu} (Z=63) : [\text{Xe}] 4f^{7} 6s^{2}$
$\text{Gd} (Z=64) : [\text{Xe}] 4f^{7} 5d^{1} 6s^{2}$
Thus, Ytterbium ($\text{Yb}$) has a completely filled $4f$ orbital.
Answer: $\text{Yb}$
$\text{La} (Z=57) : [\text{Xe}] 5d^{1} 6s^{2}$
$\text{Yb} (Z=70) : [\text{Xe}] 4f^{14} 6s^{2}$
$\text{Eu} (Z=63) : [\text{Xe}] 4f^{7} 6s^{2}$
$\text{Gd} (Z=64) : [\text{Xe}] 4f^{7} 5d^{1} 6s^{2}$
Thus, Ytterbium ($\text{Yb}$) has a completely filled $4f$ orbital.
Answer: $\text{Yb}$
Hence, the correct answer is option: 'B'.