What is an oil-in-water emulsion?

• A. Water droplets dispersed in oil
• B. A uniform mixture of oil and water
• C. Oil droplets dispersed in water
• D. Oil droplets suspended in air

Answer: (C)

An oil-in-water emulsion is when tiny droplets of oil are dispersed throughout a continuous water phase. In this setup, water is the surrounding medium and the dispersed phase is oil, so you have oil droplets suspended in water. This is different from water-in-oil, where water droplets would be dispersed in a continuous oil phase. If you tried to make a uniform mixture of oil and water without an emulsifier, they’d separate because they don’t mix, rather than form a single homogeneous phase. An aerosol—oil droplets suspended in air—is not an emulsion.