Question

Which of the following is the correct electronic configuration of sodium atom?

• A. 2, 8, 2
• B. 2, 5, 2
• C. 2, 8, 1
• D. 2, 2, 2

Answer 1

The correct option is C 2, 8, 1

Atomic number of sodium is 11. Thus, it contains 11 protons.

For a neutral atom, the number of protons is equal to the number of electrons. Hence, for sodium atom, the number of electrons = 11.
The maximum no. of electrons that can be accommodated in a shell is given by $2\times n^2$, where n represents the no. of shell.
Hence, no. of electrons in
K shell = ($2\times 1^2$) = 2 electrons
L shell = ($2\times 2^2$) = 8 electrons
Now only one electron is remaining. Thus, M shell accomodates 1 electron.

Hence, electronic configuration of sodium atom is 2, 8, 1.