Hund's rule of maximum multiplicity states that electrons occupy degenerate orbitals singly before any pairing occurs, and the singly occupied orbitals all have the same spin direction to maximize the spin multiplicity (total spin). This arrangement minimizes electron–electron repulsion by keeping electrons in separate orbitals. For three electrons in 2p: each electron enters a separate p orbital (p_x, p_y, p_z), all with the same spin (all spin-up or all spin-down). This gives ↑ in p_x, ↑ in p_y, ↑ in p_z. Option (A) is incorrect because pairing in p_x before occupying p_y and p_z violates Hund's rule. Option (B) has a paired electron in p_x while p_z is empty, again violating Hund's rule. Option (D) has mixed spins (↑ and ↓) in singly occupied orbitals, which violates the spin alignment requirement of Hund's rule. The ground state configuration described corresponds to nitrogen's 2p^3 subshell (Z=7), a classic NCERT example of Hund's rule. Plausibility check: a half-filled subshell (p^3 here) is known to be especially stable due to maximum exchange energy, consistent with all three orbitals being singly occupied with parallel spins.