Question

Assertion (A) Atoms with completely filled and half-filled subshells are stable.
Reason (R) Completely filled and half-filled subshells have symmetrical distribution of electrons and have maximum exchange energy.
The correct answer is

• A. (A) and (R) are correct, (R) is the correct explanation of (A)
• B. (A) and (R) are correct, (R) is not the correct explanation of (A)
• C. (A) is correct, but (R) is not correct
• D. (A) is not correct, but (R) is correct

Answer 1

Answer: (A)

The extra stability of half-filled and fully filled electronic configuration can be explained in terms of symmetry and exchange energy. All the orbitals of the same subshell are either completely filled or half-filled have more symmetrical distribution of electrons. Consequently, their shielding of one another is relatively small and the electrons are more strongly attracted by the nucleus. This leads to more stability of the atom.