Which statement about the zwitter ionic form of an amino acid acid is correct ?

Options

A. The zwitter ion acts only as a base
B. The zwitter ion carries an overall charge which can be positive or negative
C. The zwitter ion is neutral overall
D. The zwitter ion acts only as an acid

Explanation

To determine which statement about the zwitter ionic form of an amino acid is correct, we first need to understand what a zwitter ion is.

### Step-by-Step Solution:

1. **Understanding Amino Acids**:
- Amino acids are organic compounds that serve as the building blocks of proteins. They contain both an amino group (-NH2) and a carboxyl group (-COOH) attached to a central carbon atom.

2. **Formation of Zwitter Ion**:
- In a zwitter ionic form, the amino acid can exist in a state where the amino group is protonated (NH3+) and the carboxyl group is deprotonated (COO-).
- This results in a molecule that has both a positive charge (from the NH3+) and a negative charge (from the COO-), but the overall charge of the molecule is neutral.

3. **Analyzing the Statements**:
- **Option A**: "The zwitter ion acts as only a base."
- This is incorrect because the zwitter ion has both acidic (COO-) and basic (NH3+) characteristics.

- **Option B**: "The zwitter ion carries an overall charge which can be positive or negative."
- This is incorrect because the zwitter ion is neutral overall; it has both positive and negative charges that cancel each other out.

- **Option C**: "The zwitter ion is neutral overall."
- This is correct. The zwitter ion has no net charge as the positive and negative charges balance each other.

- **Option D**: "The zwitter ion only acts as an acid."
- This is incorrect because the zwitter ion can act as both an acid and a base due to the presence of both functional groups.

4. **Conclusion**:
- The correct statement about the zwitter ionic form of an amino acid is: **"The zwitter ion is neutral overall."**