Question

The correct statements among the following.
i. $E_{2s} (H) >\, E_{2s} (Li) <\, E_{2s} (Na) > \,E_{2s} (K)$
ii. The maximum number of electrons in the shell with principal quantum number $n$ is equal to $2n^{2}$
iii. Extra stability of half-filled subshell is due to smaller exchange energy.
iv. Only two electrons, irrespective of their spin, may exist in the same orbital are.

• A. i and ii
• B. ii and iii
• C. iii and iv
• D. i and iv

Answer 1

Answer: (A)

(i) Energy of the 2sorbital of different elements decreases as nuclear charge (equal to atomic number) of atom increases.
(ii) There are $n^{2}$ orbitals in a shell with principal quantum number $n$.
$\therefore $ total number of electrons $=2n^{2}$
(iii) Extra stability of half-filled orbitals is due to greater exchange energy
(iv) For two electrons will be in the same orbital, their spin quantum numbers must be different
It is not irrespective of their spin