Explain briefly why each of the following is not a possible set of quantum numbers for an electron in an atom. 

(a) n = 2, ℓ = 2, m_ℓ = 0
(b) n = 3, ℓ = 0, m_ℓ = −2
(c) n = 6, ℓ = 0, m_ℓ = 1