Which of the following is a liquid emulsion?

A liquid emulsion specifically refers to a mixture of two immiscible liquids, typically oil and water, where one liquid is dispersed in the other in small droplets. In the context of the choices provided, the option that represents a liquid emulsion is oil and water emulsion.

This emulsion is characterized by the tiny droplets of oil being suspended in water, along with stabilizers or emulsifiers that help maintain this mixture by preventing the oil droplets from coalescing. This principle is widely applied in various industries, including food (dressings, sauces) and cosmetics.

The other choices do not represent emulsions. Water mixed with salt is a solution where the salt dissolves completely in the water, forming a uniform liquid. Metal in solution also refers to a mixture where metal ions are dissolved in a solvent, not an emulsion. Soda water, on the other hand, comprises carbon dioxide gas dissolved in water, forming a carbonation effect, rather than mixing two separate liquid phases like an emulsion does.