Rapid sand filters are effective in removing which of the following?

Rapid sand filters are indeed effective in removing particles from water. The functioning of these filters relies on a bed of sand which captures and retains suspended solids and other particulate matter as water flows through it. The process involves mechanical straining, where larger particles are blocked by the sand grains, and interception, where smaller particles are caught within the spaces between the sand grains.

While rapid sand filters may remove some microorganisms as well, they are not primarily designed for that purpose. Their effectiveness in removing dissolved gases is minimal, as these substances do not accumulate as particles do. Similarly, while some heavy metals may be captured depending on their particulate form, rapid sand filters are not specifically designed as a treatment for heavy metals. Thus, the primary and most effective application of rapid sand filters is indeed the removal of particles from water, making it a suitable and correct answer to the question.