The type of epithelium that would best allow rapid diffusion is called

Simple squamous

Explanation:

The simple squamous epithelium is a type of epithelial tissue. It has a single layer of flattened cells. The cells of this tissue have a nucleus present in the center. The single layer of these cells is specialized to allow diffusion of substances. Simple squamous epithelium is specifically present at the sites where filtration and diffusion occurs. The endothelium of blood vessels and lymphatic vessels is made up of simple squamous epithelium. In the lungs, it allows diffusion of respiratory gases.