Step 1: Recall the concept of colloids.

• Milk is an emulsion, since fat droplets are dispersed in water.
• Butter is also a colloid but of a different type.

Step 2: Identify the type for butter.

• In butter, tiny water droplets are dispersed in solid fat.
• This type of colloid is called a Gel, i.e., liquid dispersed in solid.

Step 3: Match with options:

• (A) Aerosol → gas dispersed in liquid/solid   \(\times\)
• (B) Suspension → not a colloid, unstable mixture   \(\times\)
• (C) Sol → solid dispersed in liquid   \(\times\)
• (D) Gel → liquid dispersed in solid   \(\checkmark\)

Therefore,

\[ \text{Milk : Emulsion :: Butter : Gel} \]