Which of the following amino acids is most basic :

Options

A. `H_2N-undersetunderset(NH)(||)C-NH-CH_2CH_2CH_2-undersetunderset(NH_2)(|)CH-COOH`
B. `H_2N-undersetunderset(CH_3)(|)CH-oversetoverset(O)(||)C-NH-CH_2-COOH`
C. `HOOC-CH_2-undersetunderset(NH_2)(|)CH-COOH`
D.

Explanation

To determine which amino acid is the most basic among the given options, we will analyze the structure of each amino acid and count the number of amino (–NH2) groups present. The more amino groups an amino acid has, the more basic it is.

### Step-by-Step Solution:

1. **Identify the Amino Acids**:
We have four options (A, B, C, D) with different structures. We need to analyze each structure for the presence of amino groups.

2. **Analyze Option A**:
- Structure: NH2, C=O, NH, CH2, CH2, CH2, CH, NH2, COOH
- Count of Amino Groups:
- 2 NH2 groups (one at each end)
- 2 NH groups (one in the middle)
- Total Amino Groups: 4 amino groups.

3. **Analyze Option B**:
- Structure: NH2, CH, CH3, C=O, NH, CH2, COOH
- Count of Amino Groups:
- 1 NH2 group
- 1 NH group
- Total Amino Groups: 2 amino groups.

4. **Analyze Option C**:
- Structure: COOH, CH2, CH, NH2, COOH
- Count of Amino Groups:
- 1 NH2 group
- Total Amino Groups: 1 amino group.

5. **Analyze Option D**:
- Structure: SH, NH2, COOH
- Count of Amino Groups:
- 1 NH2 group
- Total Amino Groups: 1 amino group.

6. **Compare the Counts**:
- Option A has 4 amino groups.
- Option B has 2 amino groups.
- Option C has 1 amino group.
- Option D has 1 amino group.

7. **Conclusion**:
Since Option A has the highest number of amino groups (4), it is the most basic amino acid among the options provided.

### Final Answer:
**Option A is the most basic amino acid.**