The extra stability of half-filled subshell is due to :
(A) Symmetrical distribution of electrons
(B) Smaller coulombic repulsion energy
(C) The presence of electrons with the same spin in non-degenerate orbitals
(D) Larger exchange energy
(E) Relatively smaller shielding of electrons by one another
Indentify the correct statements :

Solution

Chemistry ma’am · 2 steps

Test each statement alone. Only (C) fails: exchange needs degenerate orbitals, not non-degenerate ones.

1. Picture the subshell. In a half-filled subshell such as p³ or d⁵, each degenerate orbital holds exactly one electron, and all those electrons have the same spin.

   Statement	Correct?	Reason
   (A) Symmetrical distribution	Yes	One electron in every orbital spreads the charge evenly around the nucleus.
   (B) Smaller coulombic repulsion	Yes	No orbital holds a pair, so there is no pairing repulsion.
   (C) Same spin in non-degenerate orbitals	No	Exchange happens between same-spin electrons in degenerate orbitals of one subshell.
   (D) Larger exchange energy	Yes	Same-spin electrons in degenerate orbitals can swap places. In d⁵ there are 10 such swaps, which lowers the energy.
   (E) Smaller mutual shielding	Yes	Electrons in one subshell shield each other poorly, so each one feels a larger nuclear pull.

2. So. (A), (B), (D) and (E) are correct and (C) is wrong. The answer is option (b).

The idea to keep. Half-filled and fully filled subshells are extra stable because of symmetry and exchange energy. Exchange always involves same-spin electrons in degenerate orbitals.

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