Explanation:

Oil and water: Oil floats on top of water. After letting a mixture of oil and water sit, the oil can be poured off of the water. In a separatory funnel, the water can be drained away from the oil.

Dirt and water: Decantation is one way to clean muddy water. Soil and debris sinks to the bottom, so clear water is poured off. Decanting water isn’t sufficient to completely purify it because some particles (like bacteria and viruses) are too light to sink with the dirt. Other particles dissolve in water (like heavy metals and pesticides). Even after decantation, other methods are needed to produce drinking water, like filtration or distillation.

Kerosene and water (or gasoline and water): The kerosene or gasoline floats above the water. Decanting this liquid is dangerous because the fuel evaporates to form flammable, toxic fumes.

Milk and cream: Decantation separates cream from milk. Cream rises to the top of the liquid and is easily skimmed off.

Precipitate from supernate: Decantation separates precipitate from supernate in a chemical reaction that yields a solid product. Decanting may be preferable to filtration for separating tiny particles from liquid.

Blood and plasma: Plasma is separated by blood by decantation using a centrifuge.