______ is the process of allowing particles in suspension in water to settle out of the suspension under the effect of gravity.

Sedimentation

The correct answer is option 3. Sedimentation.

Sedimentation is the process by which solid particles suspended in a liquid settle out of the suspension and accumulate at the bottom of the container due to the force of gravity. Here's how sedimentation works:

1. Suspension: Initially, solid particles are dispersed throughout the liquid, forming a suspension. These particles are typically insoluble and may vary in size and composition. Examples of suspended particles include dirt, sand, clay, and organic matter in water.

2. Gravity: When left undisturbed, gravity exerts a downward force on the solid particles in the suspension. This force causes the particles to settle downward through the liquid.

3. Settling:  As the solid particles settle, they gradually accumulate at the bottom of the container, forming a layer of sediment. The rate of settling depends on factors such as the size, density, and shape of the particles, as well as the viscosity and density of the liquid.

4. Clear Liquid:  Over time, the liquid above the sediment becomes clearer as the solid particles are removed from suspension. This process is crucial in various industries and natural processes, including water treatment, wastewater treatment, mining, and geological formation.

Sedimentation is often followed by decantation, which involves carefully pouring off the clear liquid from above the sediment layer, leaving the sediment behind. This allows for the separation of the solid particles from the liquid phase.

Overall, sedimentation is a simple yet effective method for separating suspended solids from a liquid by harnessing the force of gravity. It is widely used in various applications where the removal of solid particles from a liquid is necessary for further processing or purification.