In which of the following case, the forms of amino acid and pH is (are) correctly matched ?

Options

A. Alanine : `pH=3, H_(3)overset(+)(N)-underset(CH_(3))underset("| ")("C ")H-COO^(-)`
B. Leucine : `pH=10, H_(2)N-underset(CH_(2)-underset(CH_(3))underset("| ")("C ")H-CH_(3))underset("| ")(CH-COO^(-))`
C. Aspartic acid : `pH = 9, H_(2)N-underset(CH_(2)-COO^(-)" ")underset("| ")(CH-COO^(-))`
D. Lysine : `pH=3, H_(2)overset(+)(N)-underset(CH_(2)CH_(2)CH_(2)CH_(3)overset(+)(N)H_(3))underset("| ")(CH-COOH" ")`

Explanation

To solve the question regarding the correct matching of amino acids and their pH values, we will analyze each option step by step.

### Step 1: Understand the Concept of Isoelectric Point (pI) and pH
- The isoelectric point (pI) is the pH at which an amino acid exists predominantly in its zwitterionic form (neutral form).
- If the pH is less than the pI, the amino acid will predominantly exist in its cationic form (positively charged).
- If the pH is greater than the pI, the amino acid will predominantly exist in its anionic form (negatively charged).

### Step 2: Analyze Each Option

#### Option 1: Alanine
- **pI of Alanine**: 6.0
- **Given pH**: 3
- Since pH (3) < pI (6.0), the dominant form should be cationic.
- However, alanine is a neutral amino acid and does not have a dominant cationic form at this pH.
- **Conclusion**: Incorrect match.

#### Option 2: Leucine
- **pI of Leucine**: 5.98
- **Given pH**: 10
- Since pH (10) > pI (5.98), the dominant form should be anionic.
- Leucine is a neutral amino acid, and at this pH, it will exist in its anionic form.
- **Conclusion**: Correct match.

#### Option 3: Aspartic Acid
- **pI of Aspartic Acid**: 2.77
- **Given pH**: 9
- Since pH (9) > pI (2.77), the dominant form should be anionic.
- Aspartic acid is an acidic amino acid, and at this pH, it will exist in its anionic form.
- **Conclusion**: Correct match.

#### Option 4: Lysine
- **pI of Lysine**: 9.74
- **Given pH**: 3
- Since pH (3) < pI (9.74), the dominant form should be cationic.
- Lysine is a basic amino acid, and at this pH, it will exist in its cationic form.
- **Conclusion**: Correct match.

### Final Answer
The amino acids and their pH that are correctly matched are:
- **Leucine (Option 2)**
- **Aspartic Acid (Option 3)**
- **Lysine (Option 4)**

Thus, the correct options are **2, 3, and 4**.

---