Question

what type of molecule could simply diffuse through the cell membrane?
starch
oxygen
ions

Explanation:

Simple diffusion through the cell membrane occurs for small, non - polar, or lipid - soluble molecules. Starch is a large polysaccharide and cannot pass through by simple diffusion. Ions are charged and require protein channels or carriers for transport (facilitated diffusion or active transport). Oxygen ($O_2$) is a small, non - polar molecule that can pass through the lipid bilayer of the cell membrane via simple diffusion.

Answer:

oxygen