Explain briefly why each of the following is not a possible set of quantum numbers for an electron in an atom. In each case, change the incorrect value (or values) to make the set valid. 

(a) n = 2, ℓ = 2, m_ℓ = 0, ms = +1⁄2
(b) n = 2, ℓ = 1, m_ℓ = −1, ms = 0
(c) n = 3, ℓ = 1, m_ℓ = −2, ms = +1⁄2