What will be the nature of existence of an amino acid (containing one amino and one carboxylic acid group) in solution of `pH lt pK_(a_(1))`?

Options

A. It exists an anion
B. It exists as cation
C. It exists as zwitter ion
D. It exists as neutral species with no charge

Answer

To determine the nature of existence of an amino acid (which contains one amino group and one carboxylic acid group) in a solution where the pH is less than the pKa, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structure of Amino Acids**:
- Amino acids have two functional groups: an amino group (-NH2) and a carboxylic acid group (-COOH).
- In solution, they can exist in different forms depending on the pH.

2. **Defining Zwitterion**:
- At a certain pH, amino acids can exist as zwitterions, where the amino group is protonated (NH3+) and the carboxylic group is deprotonated (COO-).
- However, the zwitterion form is typically observed at the isoelectric point (pI) of the amino acid.

3. **Analyzing pH and pKa Relationship**:
- The pKa is the measure of the acidity of the carboxylic acid group.
- When the pH of the solution is less than the pKa of the carboxylic acid group, it means that the environment is more acidic.

4. **Protonation State at Low pH**:
- In an acidic environment (pH < pKa), the carboxylic acid group will remain protonated (COOH), and the amino group will also be protonated (NH3+).
- Therefore, the amino acid will exist predominantly in its cationic form: NH3+ - CH - COOH.

5. **Conclusion**:
- Since the pH is less than the pKa, the amino acid will exist as a cation (positively charged species).

### Final Answer:
The nature of existence of the amino acid in a solution where pH < pKa is that it exists as a **cation**.

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