Final answer:
Oxygen (O2) can passively penetrate the plasma membrane through simple diffusion as it is a small, non-charged molecule. Polar substances, charged particles, and large molecules would require facilitated transport to cross the membrane.
Step-by-step explanation:
The question "Which of the following is able to passively penetrate the plasma membrane?" relates to how different substances interact with the cell membrane. The answer is A. O2, as oxygen molecules have no charge and can pass through cell membranes by simple diffusion. This is because they are small and non-charged molecules, unlike small charged particles, large polar molecules, and ions that cannot pass through the membrane without help.
Polar substances and ions such as sodium, potassium, calcium, and chloride require special means of penetration, like facilitated transport, because their charge or size prevents them from diffusing through the phospholipid bilayer of the plasma membrane. As a result, they need help from transport proteins or channels to move across.