Assertion : A protein is a heteropolymer.
Reason : Dietary proteins are the source of non-essential amino acids.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion:**
- The assertion states that "A protein is a heteropolymer."
- A heteropolymer is a type of polymer that is made up of different types of monomers. In the case of proteins, the monomers are amino acids.

2. **Identifying the Monomers:**
- Proteins are composed of 20 different types of amino acids. These amino acids can combine in various sequences to form different proteins.
- Since proteins can be made from a combination of these 20 amino acids, they qualify as heteropolymers.

3. **Conclusion on the Assertion:**
- Since proteins are indeed made from different types of amino acids, the assertion that "A protein is a heteropolymer" is true.

4. **Understanding the Reason:**
- The reason states that "Dietary proteins are the source of non-essential amino acids."
- Non-essential amino acids are those that the body can synthesize on its own. There are 10 non-essential amino acids that the human body can produce.

5. **Evaluating the Reason:**
- Dietary proteins provide essential amino acids, which the body cannot synthesize and must be obtained from food. Non-essential amino acids are synthesized by the body and do not need to come from dietary sources.
- Therefore, the statement that dietary proteins are the source of non-essential amino acids is false.

6. **Final Conclusion:**
- The assertion is true, but the reason is false. Thus, the correct answer is that the assertion is true and the reason is false.

**Final Answer:**
- Assertion is true, but the reason is false.

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