Which technique is used for separating mixtures that involves passing a liquid through a filter?

The technique used for separating mixtures by passing a liquid through a filter is known as filtration. This process works by utilizing a porous barrier that allows the liquid part of the mixture (the filtrate) to pass through while retaining solid particles (the residue) on the filter. This is particularly effective for separating substances based on their size or physical state, making it a common method in both laboratories and various industrial processes.

Filtration is useful in many applications, such as purifying a liquid by removing suspended solids and separating components of mixtures where one component is in solid form and the other is liquid. For instance, if a mixture of sand and water is filtered, the sand will remain on the filter paper, while the water will pass through.

The other techniques mentioned in the question serve different purposes. Evaporation is used to separate a dissolved solid from a liquid, typically by heating the mixture to allow the liquid to turn into vapor. Crystallization is a method used to form solid crystals from a solution, often used to purify compounds. Magnetism, on the other hand, is applicable to separate magnetic materials from non-magnetic ones, rather than dealing with mixtures involving liquids in a filtering process.