What does reverse osmosis effectively reject when functioning correctly?

Reverse osmosis is a highly effective water purification process that utilizes a semipermeable membrane to separate contaminants from water. When functioning correctly, it primarily targets and rejects a wide range of impurities, including bacteria, viruses, and pyrogenic materials.

The reason this option is correct lies in the mechanism of reverse osmosis. The membrane used in this process has very tiny pores that allow water molecules to pass through while blocking larger particles, including microorganisms like bacteria and viruses. This capability makes reverse osmosis a popular choice for producing safe drinking water by significantly reducing biological contaminants that could pose health risks.

In contrast, although reverse osmosis can remove some organic pollutants and sediments, as well as other substances like chlorine, it is particularly notable for its effectiveness against microbial contaminants, which are critical for maintaining water safety. The rejection of gases and volatile compounds is not a primary function of reverse osmosis, as those substances can sometimes pass through the membrane depending on their size and structure.