What is the maximum number of electrons that can be identified with each of the following sets of quantum numbers? In some cases, the answer may be “none.” In such cases, explain why “none” is the correct answer.

(a) n = 3
(b) n = 3 and ℓ = 2
(c) n = 4, ℓ = 1, m_ℓ = −1, and m_s = +1⁄2
(d) n = 5, ℓ = 0, m_ℓ = −1, m_s = +1⁄2