How many maximum electrons can the M shell have?

Correct option is A

The M shell, also known as the third principal shell, can have a maximum of 18 electrons. This is because the M shell contains three subshells: s, p, and d.
The s subshell can hold a maximum of 2 electrons, the p subshell can hold a maximum of 6 electrons, and the d subshell can hold a maximum of 10 electrons. Therefore, the total maximum number of electrons that can be accommodated in the M shell is 2 + 6 + 10 = 18.