Which of these is an example of an emulsion?

• A. Butter
• B. Oil
• C. Saltwater
• D. Mayonnaise

Answer: (D)

An emulsion is a mixture where one liquid is dispersed as tiny droplets within another liquid that they don’t mix with, kept stable by an emulsifier. Mayonnaise fits this because oil droplets are dispersed throughout a water-based phase, and egg yolk provides emulsifiers (like lecithin) that stabilize those droplets so the mixture doesn’t separate. Saltwater is a single homogeneous solution, not droplets of one liquid in another. Oil alone isn’t mixed with another immiscible liquid. Butter isn’t described as a simple emulsion the way mayonnaise is in basic science contexts, so mayonnaise stands out as the clear example of an emulsion.