Step 1: Definition of an emulsion.
An emulsion is a colloidal mixture where one liquid is dispersed in another liquid with which it is immiscible. Examples of emulsions include milk and mayonnaise.
Step 2: Explanation of options.
Butter: Butter is a colloid but not an emulsion; it is a water-in-fat dispersion.
Mist: Mist is an example of an aerosol, not an emulsion.
Milk: Milk is an emulsion where fat globules are dispersed in water.
Jellies: Jellies are examples of gels, not emulsions.
Step 3: Conclusion.
Among the given options, milk is the correct example of an emulsion.