JEE Main · 2004 · 24 Apr 2004 · Offline · Atomic Structure

Consider the ground state of Cr atom

(Z = 24)

. The number of electrons with the azimuthal quantum numbers

l = 1

and 2 are respectively

Answer: (D)

Solution

Chromium at

Z = 24

takes the exceptionally stable arrangement

1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{1} 3 d^{5}

, where one 4s electron has slipped into 3d to give a half-filled d subshell. The electrons with

l = 1

live in the p subshells,

2 p^{6}

and

3 p^{6}

, which between them hold twelve electrons. The electrons with

l = 2

live in the d subshell, and

3 d^{5}

supplies five. So the two counts come to twelve and five.

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option