HINT: Emulsions are liquid-liquid colloidal system.

Explanation:

Step 1: 

Emulsifying agent: The substance which acts as a stabilizer (which prevents separation of two non-mixing liquids) for emulsions, is known as an emulsifying agent.

Emulsifying agents are also known as emulsifiers. For o/w type emulsions, the emulsifying agent used is proteins. For milk which is an example of oil i.e. fat in water, the emulsifying agent is protein.

And for the water in oil i.e. w/o type emulsions, emulsifying agents are lampblack, long chains alcohols, and Heavy metal salts of fatty acids. Hence, the emulsifying agent used in o/w emulsion is protein.

Step 2:  

Emulsions are can’t be broken by adding more amount of dispersion medium and adding emulsifying agent as on adding more amount of dispersion medium they become dilute and on adding emulsifying agent they get stabilizes.