Question

Indicate the number of unpaired electrons in : (a) P, (b) Si, (c) Cr, (d) Fe and (e) Kr.

NCERT Class XII
Chemistry - Main Course Book I

Chapter 2. Structure of Atom

Answer 1

atomic numbers and electronic configurations are:
P  : 15 : 1s2 2s2  2p6   3s2  3p3                 :  3 in the 3p orbital
Si : 14 : 1s2 2s2 2p6  3s2  3p2                   :  2 in 3p orbital
Cr: 24  : 1s2  2s2  2p6 3s2 3p6 4s2 3d4      :  4 in the 3d orbital..
Fe: 26 : 4s2  3d6             4 in the 3d orbital..  2 electrons are paired in 3d orbital.
Kr: 36  :   4s2 3d10  4p6        there are not any -- it is an ideal gas config..
           as all orbitals are full and paired.