Answer: n = 4.
Explanation:
1) The main energy level is represented by the principal (main) quantum number, n. It can be 1, 2, 3, 4, 5,6, or 7. It is the period number in the periodic table.
2) The next quantum number is the Azimuthal quantum number (ℓ), also known as angular quantum number. It indicates the subshell (sublevel) or type of orbital.
This quantun number may be:
s, p, d, or f.
3) For n = 1, there is only one ℓ number: 0; which is the orbital s
For n = 2, there are two possible ℓ numbers: 0 and 1; which are the orbitals s and p.
For n = 3, there are three possible ℓ numbers: 0, 1, and 2, which are the orbitals s, p, and d:
For n = 4, there are four possible ℓ numbers:0, 1, 2, and 3; which are the orbitals s, p, d, and f.
So, the f sublevel appears first time when n = 4, i.e the number of the lowest energy level that contains an f sublevel is 4.
