What is the process called when a liquid or fat is turned into a solid at room temperature by adding hydrogen?

The process of turning a liquid or fat into a solid at room temperature by adding hydrogen is known as hydrogenation. This chemical reaction involves the addition of hydrogen molecules to unsaturated fats, which typically remain liquid at room temperature. As hydrogen is added, the unsaturated bonds in the fat are converted into saturated bonds, resulting in a solid or semi-solid product, such as margarine.

Emulsification refers to the mixing of two immiscible liquids, like oil and water, which does not involve changing the state of a fat. Fermentation is a metabolic process where microorganisms convert sugars into acids, gases, or alcohol, which is unrelated to the alteration of fats. Dehydration involves removing water from a substance, typically to preserve it or concentrate flavors, and also does not involve the transformation of fat from liquid to solid. Hence, hydrogenation is the correct term for this process.