In which of the following actinoid elements \(6d\) subshell is vacant?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Pu, Plutonium
Plutonium (Z = 94) is 5f67s2: all its electrons beyond the radon core are in 5f and 7s, so the 6d subshell is vacant. Pa, Np and Lr each have one electron in 6d.
NCERT (2026-27 edition):
Some Properties of Actinium and Actinoids (rows of Table 4.10)
| Atomic Number | Name | Symbol | Electronic configurations (M) |
|---|---|---|---|
| 91 | Protactinium | Pa | 5f26d17s2 |
| 93 | Neptunium | Np | 5f46d17s2 |
| 94 | Plutonium | Pu | 5f67s2 |
| 103 | Lawrencium | Lr | 5f146d17s2 |