`H_(2)N-underset(R )underset(|)overset(H)overset(|)C-COOH` is general formula of amino acid. Here R stands is

Options

A. An amino acid
B. A carboxylic group
C. A variable group
D. A hydroxyl group.

Answer

To solve the question regarding the structure of an amino acid represented by the formula `H₂N-R|C-COOH`, we need to identify what the "R" stands for in this context. The "R" in the general formula of an amino acid represents the variable group that distinguishes different amino acids from one another.

### Step-by-Step Solution:

1. **Understand the Structure of Amino Acids**:
- Amino acids have a general structure that includes an amino group (NH₂), a carboxyl group (COOH), and a central carbon atom (C) to which these groups are attached. The "R" group is attached to this central carbon.

2. **Identify the Components**:
- In the given structure, `H₂N` represents the amino group.
- `COOH` represents the carboxyl group.
- The central carbon (C) connects these two groups and the "R" group.

3. **Define the "R" Group**:
- The "R" group is known as the variable group or side chain. It can vary between different amino acids, which is what gives each amino acid its unique properties.
- The nature of the "R" group can include various functional groups, such as additional amino groups, carboxyl groups, hydroxyl groups, or hydrocarbon chains.

4. **Conclusion**:
- Since the question asks what "R" stands for in the context of amino acids, the correct answer is that "R" represents the **variable group**.

### Final Answer:
R stands for the **variable group**.