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

\(4l + 2\)

The correct answer is option 4. \(4l + 2\).

\(\text{Quantum number:}\) 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.

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 \((2l + 1)\).

Maximum electrons a subshell can accommodate is \(2\)

Therefore, the total number of electrons in a subshell is \(2 (2l + 1 ) = (4l + 2)\)

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