**Answer: orbital shape.**

**Justification:**

1) There are **four quantum numbers** to describe the electrons. These are:

i) Principal quantum number (n)

ii) Azimuthal quantum number (ℓ), also called angular momentum quantum number.

iii) Magnetic quantum number (m)

iv) Spin quantum number (s)

2) The** principal quantum numbe**r tells the **main energy level**. It can be 1, 2, 3, 4, 5, 6, 7. It is related with the orbial size. 1 is a small orbital, 7 is a big orbital.

2) The **Azimuthal quantum number (ℓ) or angular momentum quantum number **may be a number between 0 and n - 1.

It tells the **kind of orbital, which is its shape**

The correspondence is:

**0 = s orbital, **

**1 = p orbital, **

**2 = d orbital, **

**3 = f orbital.**

3) Magnetic quantum number (m) tells the orientation. It can be from - ℓ to + ℓ

For example when ℓ = 1, the orbital is p, and the magnetic quantum number may be -1, 0, or +1, which correspond to px, py, pz: the orientation of the p orbital in the space.

4) **Spin quantum number (s) **can be either +1/2 or -1/2.