The incorrect structure of glycine at given `pH` are `:`

Options

A. `H_(3)overset(o+)(N)CH_(2)-underset(underset(O)(||))(C)-OH" at"pH=2.0`
B. `H_3overset(o+)(N)CH_(2)-underset(underset(O)(||))(C)-O^(ɵ)" at "pH=6.0`
C. `H_(2)NCH_(2)-underset(underset(O)(||))(C)-O^(ɵ)" at "pH=9`
D. `H_(2)NCH_(2)-underset(underset(O)(||))(C)-OH" at "pH=12`

Explanation

To determine the incorrect structure of glycine at a given pH, we need to understand how glycine behaves at different pH levels, particularly in relation to its isoelectric point (pI).

### Step-by-Step Solution:

1. **Understand Glycine Structure**: Glycine is the simplest amino acid with the following structure:
- Amino group: -NH2
- Carboxyl group: -COOH
- Hydrogen atom: -H
- R group: In glycine, the R group is simply a hydrogen atom (H).

2. **Identify the Isoelectric Point (pI)**: The pI of glycine is approximately 6. This is the pH at which glycine exists predominantly as a zwitterion (a molecule with both positive and negative charges).

3. **Analyze Glycine at Different pH Levels**:
- **At pH < pI (pH < 6)**: Glycine exists in its cationic form:
- Structure: NH3^+ - CH(R) - COOH
- Here, the carboxyl group is protonated (-COOH) and the amino group is positively charged (-NH3^+).

- **At pH = pI (pH = 6)**: Glycine exists as a zwitterion:
- Structure: NH3^+ - CH(R) - COO^-
- The amino group is positively charged, and the carboxyl group is negatively charged.

- **At pH > pI (pH > 6)**: Glycine exists in its anionic form:
- Structure: NH2 - CH(R) - COO^-
- The amino group is neutral (-NH2), and the carboxyl group is negatively charged (-COO^-).

4. **Determine the Incorrect Structure at pH 12**:
- At pH 12, which is greater than the pI of glycine, the structure should be:
- NH2 - CH(R) - COO^-
- If any structure shows the cationic form (NH3^+ - CH(R) - COOH) at this pH, it would be incorrect.

5. **Conclusion**: The incorrect structure of glycine at pH 12 would be the one that shows the cationic form (NH3^+ - CH(R) - COOH) since at this pH, glycine should exist in its anionic form.

### Final Answer:
The incorrect structure of glycine at pH 12 is: **NH3^+ - CH(R) - COOH**.