Which among the following food items is not an example of an emulsion type colloid?

Introduction / Context:
This question tests understanding of colloids and emulsions in everyday foods. Many dairy products are emulsions, where tiny droplets of one liquid are dispersed in another immiscible liquid. Recognising which items are emulsions and which are not helps students apply abstract concepts to common substances like milk, butter, cream, and curd.

Given Data / Assumptions:

• Options include chocolate milk, butter, whipped cream, and curd.
• Emulsion is defined as a colloid in which both dispersed phase and dispersion medium are liquids.
• Dairy products often involve fat dispersed in water or vice versa.

Concept / Approach:
Milk is a classic example of an oil in water emulsion, with fat droplets dispersed in water. Chocolate milk is milk with added cocoa, so it still largely behaves as an emulsion. Butter is considered a water in oil emulsion, with tiny water droplets dispersed in fat. Whipped cream originates from cream, which is itself an emulsion, and incorporates air to form a foam but still relies on the underlying emulsion structure. Curd or yoghurt, on the other hand, is formed by coagulation of proteins creating a gel network, not by liquid droplets dispersed in another liquid, so it is better classified as a gel rather than a true emulsion.

Step-by-Step Solution:
Step 1: Analyse chocolate milk. Milk is an emulsion of fat in water. Adding chocolate powder does not change the basic emulsion nature, so chocolate milk remains a type of emulsion. Step 2: Analyse butter. Butter consists of water droplets dispersed in fat, which is a water in oil emulsion. Step 3: Analyse whipped cream. Whipped cream is formed by whipping cream, an emulsion of fat in water, introducing air to create a foam but still based on an emulsion system. Step 4: Analyse curd. Curd is formed when milk proteins coagulate into a solid network trapping water and fat. This is more accurately described as a gel, not liquid in liquid emulsion. Therefore, curd is the item that is not an example of an emulsion.

Verification / Alternative Check:
Standard colloid classification lists milk, cream, butter, and mayonnaise as emulsions. Curd is usually not grouped with emulsions but with gels, because its continuous phase is solid like and not simply a liquid dispersion. This classification supports the conclusion that among the given options, curd is the one that does not fit the definition of an emulsion.

Why Other Options Are Wrong:
Option A: Chocolate milk is milk based and therefore an oil in water emulsion with added suspended cocoa solids. Option B: Butter is a water in oil emulsion where water droplets are dispersed in solidified fat. Option C: Whipped cream is a foam built on an underlying emulsion of fat in water, so it is considered an emulsion derived product.

Common Pitfalls:
Students may think that curd is similar to milk and thus must also be an emulsion. However, the key difference is that curd formation involves coagulation of casein proteins into a semi solid framework, making it a gel. Another pitfall is to ignore the precise definition of an emulsion and group all dairy products together without considering their microstructure.

Final Answer:
The food item that is not an example of an emulsion is Curd.