Question

oxygen and carbon dioxide are nonpolar molecules while water is a polar molecule. which of these must use facilitated diffusion to move across the cell membrane? oxygen and carbon dioxide molecules water molecules

Explanation:

Facilitated diffusion is a process where molecules pass through the cell membrane with the help of transport proteins. Non - polar molecules like oxygen ($\ce{O2}$) and carbon dioxide ($\ce{CO2}$) can pass through the non - polar lipid bilayer of the cell membrane by simple diffusion because they are soluble in the lipid environment. Polar molecules like water ($\ce{H2O}$) have difficulty passing through the non - polar lipid bilayer. Water molecules are small but polar, and they use facilitated diffusion (through aquaporins, which are specific water - channel proteins) to move across the cell membrane more efficiently.

Answer:

water molecules