Which one would be called a radioisotope?

A radioisotope is a radioactive isotope.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.