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Non-polar molecules diffuse faster in trans-membrane diffusion, a kind of facilitated transport. These molecules can easily diffuse throughbiological membranesdepending on the concentration gradient across them.

The slower to quicker diffusion is explained by the diffusionover the membrane. The polarity of the molecule causes diffusion. The faster the molecule diffusion through the membrane, the lower the molecule's polarity.

Because Acetamide is a non-polar chemical, it diffuses over the membrane. It is ranked second because Butyramide, a less polar compound, is included in this series. It possesses a polar molecule that is much less polar than urea and Acetamide, and it can diffuse much faster than the other two substances. As a result, it is ranked third.

The chemical urea is very polar. The C-N bond in urea is single, whereas the C=O bond is double. This creates a 120-degree angle, which causes the molecule to move in a dipole fashion. Urea is classified as a polar molecule due to its dipole movement. Due to its strong polarity, it diffuses slowly across the cell membrane.

Hence, the rate of transmembrane diffusion from lowest to highest is given as Urea, Butyramide and Acetamide.