Maximum number of electrons in a subshell of an atom is determined by the following:

Hint

Quantum number: It is defined as the set of numbers which describes the position and energy of electrons in an atom. There are four quantum numbers: principal, azimuthal, magnetic and spin quantum numbers.

Explanation

Step 1: Determine the maximum number of subshells

The principle quantum number ($n$) describe the distance between the nucleus and the electrons.
The azimuthal quantum number ($l$) is given by ($n-l$)

We know that the maximum number of subshells is equal to is $\left(2l+1\right)$.

Step 2: Determine the maximum number of electrons in a subshell
Maximum electrons a subshell can accommodate is $2$

Therefore, the total number of electrons in a subshell is

$2\left(2l+1\right)=\left(4l+2\right)$

Thus, maximum number of electrons in a subshell is $(4l+2)$

Final answer

The correct answer is option (D).