Which of the following are least likely to diffuse through the phospholipid bilayer of a cell membrane?

large hydrophobic molecules
small hydrophobic molecules
carbon dioxide
small ions

Small ions are least likely to diffuse through the phospholipid bi layer of a cell membrane.

Option D

Explanation:

The structure as well the chemical composition of the bi layer is involved in the determination of entry and exit of molecules across the membrane. This membrane considers the size and charge of the substance as factors to allow for diffusion.

The layer is highly penetrable to non-polar (fat-solvent) particles. The permeability of the layer to polar (water dissoluble) atoms is extremely low, and  penetrability to charged sub-atomic species such as ions are very low despite their size.

Thus it can be inferred that hydrophobic molecules regardless of their size has a high rate of diffusion whereas ions regardless of their size have a low rate of diffusion.