1. Energy Level (Shell):

* Principal Quantum Number (n): This number defines the electron's energy level. Higher 'n' values indicate higher energy levels, further from the nucleus. For example, an electron in the first shell (n=1) has lower energy than an electron in the second shell (n=2).

2. Subshell (Orbital):

* Angular Momentum Quantum Number (l): This number describes the shape of the electron's orbital. For a given 'n', there are multiple subshells:

* l = 0: s orbital (spherical)

* l = 1: p orbital (dumbbell shaped)

* l = 2: d orbital (more complex shapes)

* l = 3: f orbital (even more complex shapes)

* Magnetic Quantum Number (ml): This number specifies the orientation of the orbital in space. For example, a p orbital has three possible orientations (ml = -1, 0, +1).

3. Spin:

* Spin Quantum Number (ms): This number describes the intrinsic angular momentum of an electron, which is quantized and referred to as "spin." An electron can spin "up" (ms = +1/2) or "down" (ms = -1/2).

To summarize:

* Electrons in the same atom can have different energy levels (n).

* Within a given energy level, electrons can occupy different subshells (l) and orbitals (ml).

* Finally, each electron has its own unique spin (ms).

Pauli Exclusion Principle:

* The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers (n, l, ml, ms). This principle ensures that each electron occupies a unique state within the atom.