Consider the following pairs of electrons
(A) (a) n = 3, l = 1, m₁ = 1, mₛ = + 1/2
(b) n = 3, 1 = 2, m₁ = 1, mₛ = + 1/2
(B) (a) n = 3, l = 2, m₁ = -2, mₛ = -1/2
(b) n = 3, l = 2, m₁ = -1, mₛ = -1/2
(C) (a) n = 4, l = 2, m₁ = 2, mₛ = + 1/2
(b) n = 3, l = 2, m₁ = 2, mₛ = + 1/2
The pairs of electrons present in degenerate orbitals is/are :

Solution

Chemistry ma’am · 3 steps

Degenerate means same subshell: check that both n and l match, and ignore mₗ and mₛ.

1. What degenerate means. Degenerate orbitals have the same energy. In an atom, orbitals of the same subshell (same n and same l) are degenerate, whatever their mₗ values. mₛ belongs to the electron, not the orbital, so it plays no part.

   Pair	Electron (a)	Electron (b)	Degenerate?
   (A)	n = 3, l = 1: 3p	n = 3, l = 2: 3d	No, l differs
   (B)	n = 3, l = 2: 3d	n = 3, l = 2: 3d	Yes, same subshell
   (C)	n = 4, l = 2: 4d	n = 3, l = 2: 3d	No, n differs

2. Pair B. Both electrons are in 3d orbitals. Their mₗ values, -2 and -1, only pick out two different 3d orbitals, and those have the same energy.
3. So. Only pair (B) has electrons in degenerate orbitals, which is option (b).

The idea to keep. Degeneracy is decided by n and l together. Same n and l means same subshell, same energy. mₗ only names which orbital it is, and mₛ is about the electron.

Answer from the NTA final answer key. Solution by PrepWiser.