A

Step 1: Identify the given quantum numbers for an electron. For a 3d electron, the principal quantum number (n) is 3 and the azimuthal quantum number (l) is 2 (as d-orbitals correspond to l = 2).
Step 2: Analyze the options based on quantum number rules. The magnetic quantum number (m_l) for d-orbitals can take values of -2, -1, 0, +1, or +2.
Step 3: The electron spin quantum number (m_s) can be +1/2 or -1/2.
Step 4: From the options:
(a) n = 3, l = 2, m_l = +1, m_s = -1/2 (fits the criteria)
(b) n = 3, l = 2, m_l = +2, m_s = -1/2 (fits the criteria)
(c) n = 3, l = 1 (not valid as this does not correspond to 3d)
(d) n = 3, l = 0 (not valid as does not correspond to 3d)
Therefore, the possible valid quantum numbers that correspond to the 3d electron can be given in option (a) as valid.
Therefore, A.