Question

The number of unpaired electrons in chromium atom are:
A. 2
B. 3
C. 4
D. 6

Answer 1

Hint: Chromium is a chemical element represented by the symbol Cr. It is steel grey in color, lustrous in nature, hard and brittle transition element. Chromium is the first element of group 6 and has many applications due to its anti-corrosive nature.

Complete answer:
Unpaired electron can be defined as an electron which occupies an orbital of an atom in single form rather than present as a part of the electron pair. Compounds in which electrons are not paired are known as unpaired electrons and these are very reactive in nature.
Atomic number of chromium is 24 now to find out the number of unpaired electrons we have to know about the electronic configuration of an atom. Electronic configuration of an atom gives us the idea about the distribution of electrons and electronic configuration of chromium is taken as special case as one electron is transferred in 3d orbital from 4s orbital so the electronic configuration of chromium can be written as: $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{5}}4{{s}^{1}}$, hence from this we can see that 5 electrons in 3d orbital and 1 electron in 4s orbital is unpaired in nature so the total number of unpaired electrons in chromium is 6.

Option D is the correct answer.

Note:
Each atomic orbital of an electron has capacity to contain two electrons which are of opposite spin value i.e. if one electron is in the state of clockwise then another will be in anticlockwise state and this was explained by Pauli exclusion principle.