The electron are distributed around the nucleus in various energy levels shells, subshells and orbitals. A set of quantum numbers completely describe the position and total energy of electron in an atom. The various permitted values of quantum numbers are :
principal, `n = 1,2,3,4......`
azimuthal , `l = 0,1,2,....(n -1)`
magnetic, `m_l = -l .....0 .....+ l`
spin, `m_s = +1//2 and -1//2`.
How many electrons are possible in all sub-shells with `n + l = 4` ?

Explanation

To determine how many electrons are possible in all sub-shells with the condition \( n + l = 4 \), we will follow these steps:

### Step 1: Understand the Quantum Numbers
The quantum numbers consist of:
- Principal quantum number (\( n \)): \( n = 1, 2, 3, 4, \ldots \)
- Azimuthal quantum number (\( l \)): \( l = 0, 1, 2, \ldots, (n - 1) \)
- Magnetic quantum number (\( m_l \)): \( m_l = -l, \ldots, 0, \ldots, +l \)
- Spin quantum number (\( m_s \)): \( m_s = +\frac{1}{2}, -\frac{1}{2} \)
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