Answer :
In determining the order of energy levels for orbitals in a Li²⁺ ion, the electron configuration and relative energy levels of the orbitals need to be considered.
For Li²⁺, we focus on understanding the energy levels of the orbitals. The electron in a single electron species like Li²⁺ (a hydrogen-like ion) will occupy orbitals based on the principal quantum number (n) and the angular quantum number (l), which determine the energy.
The energy levels for a given principal quantum number (n) in hydrogen-like single electron species are determined as:
- Orbitals with the same n have the same energy.
Therefore:
- For n=3, all orbitals (3s, 3p, and 3d) will have the same energy.
- For n=4, all orbitals (4s and 4p) will also have the same energy.
- Orbitals with a lower principal quantum number (n) are lower in energy than those with a higher n value.
This means for Li²⁺:
- 3s = 3p = 3d
- and 4s = 4p are higher in energy compared to the 3rd shell orbitals.
Thus, option (b) "3s = 3p = 3d < 4s = 4p" is the correct answer, as it properly reflects the energy order of these orbitals in a Li²⁺ ion.
