orbitals   Â
Explanation:
Each orbital may contain a maximum of two electrons.
The energy level is the principal quantum number: 1, 2, 3, 4, 5, 6, 7.
The principal quantum number limits the kind of orbital (â„“ ) and the number of orbitals (mâ„“ ).
I. Principal quantum number, n = 1
 Angular or orbital quantum number : ℓ = 0 ⇒ ortibal s
 Magnetic quantum number:  mℓ = 0
                 ⇒ number of orbitals 1 ⇒ number of electrons: 2
            Â
II. Principal quantun number, n = 2
 Angular or orbital quantum number : ℓ = 0 and 1 ⇒ ortibal s and p
 Magnetic quantum number: Â
                      for ℓ:  mℓ = 0: 1 s ortibal
                      for ℓ = 1: mℓ = -1, 0, and +1:  3 p ortitals
                 ⇒ number of orbitals 4 ⇒ number of electrons: 8
III. Principal quantun number, n = 3
  Angular or orbital quantum number : ℓ = 0, 1, and 2 ⇒ ortibal s, p and d
  Magnetic quantum number: Â
                      for ℓ:  mℓ = 0: 1 s ortibal
                      for ℓ = 1: mℓ = -1, 0, and +1:  3 p ortitals
                      for ℓ = 2: mℓ = -2, -1, 0, +1, and +2:  5 d ortitals
                 ⇒ number of orbitals 9 ⇒ number of electrons: 18
IV. Principal quantun number, n = 4
  Angular or orbital quantum number : ℓ = 0, 1, 2, and 3 ⇒ ortibal s, p, d and f
  Magnetic quantum number: Â
                      for ℓ:  mℓ = 0: 1 s ortibal
                      for ℓ = 1: mℓ = -1, 0, and +1:  3 p ortitals
                      for ℓ = 2: mℓ = -2, -1, 0, +1, and +2:  5 d ortitals
                      for ℓ = 3: mℓ = ±3, ±2, ±1, and 0: 7 f ortitals
                 ⇒ number of orbitals 16 ⇒ number of electrons: 32.
Thus, you have:
energy level, n   maximum number of   maximum number of
               orbitals              electrons
   1              1                    2
   2              4                   8
   3              9                   18
   4              16                  32
Those numbers follow a rule: n² and 2n². You can verify that the previous numbers are in accordance with those formulas.