For each set of quantum number conditions for the electrons in an atom, determine the number of electrons satisfying those conditions.
a) n = 3, l = 2, m_l = 0, m_s = -1/2
b) n = 4, l = 2, m_l = -1
c) n = 4, l = 2
d) n = 3
e) n = 4, l = 1, m_s = +1/2