According to the Pauli exclusion principle and quantum mechanics, an orbital can accommodate a maximum of two electrons, and these electrons must have opposite spins. The p-orbital is no exception to this rule. In an atom, the p-orbitals are degenerate, meaning they have the same energy level in a given shell. Each p-orbital (p_x, p_y, and p_z) can accommodate 2 electrons, making a total of 6 electrons for all three p-orbitals in a subshell having opposite spins. However, focusing on any single p-orbital, it can only accommodate two electrons with opposite spins, as they have to obey the Pauli exclusion principle, which states that no two electrons in an atom can have the same set of four quantum numbers. Therefore, the correct answer is:

Option D: two electrons with opposite spins.