Amino acids are classified as acidic, basic or netural depending upon the relative number of amino and carboxyl groups in their molecule. Which of following are acidic ?
(i)`(CH_(3))_(2)OH-underset(NH_(2))underset(|)CH-COOH`
(ii)`HOOC-CH_(2)-CH_(2)-underset(NH_(2))underset(|)CH-COOH`
(iii) `H_(2)N-CH_(2)-CH_(2)-CH_(2)-COOH`
(iv)`HOOC-CH_(2)-underset(NH_(2))underset(|) CH-COOH`

Options

A. (ii) and (iv)
B. (iii) and (iv)
C. (i)nad (ii)
D. (ii) and (iii)

Answer

To determine which of the given amino acids are acidic, we need to analyze the structures based on the presence of carboxylic acid groups. Acidic amino acids typically have one or more carboxylic acid groups in their side chains. Let's evaluate each option step by step.

### Step-by-Step Solution:

1. **Identify the Structures**:
- (i) `HOOC-CH(CH3)2-NH2`
- (ii) `HOOC-CH2-CH2-NH2-COOH`
- (iii) `NH2-CH2-CH2-CH2-COOH`
- (iv) `HOOC-CH(NH2)-COOH`

2. **Check Each Structure for Carboxylic Acid Groups**:
- **(i)**: The structure has one carboxylic acid group (`-COOH`) at the end. However, the side chain contains an alcoholic group (`-OH`), not another carboxylic acid. Therefore, this amino acid is **not acidic**.
- **(ii)**: This structure has two carboxylic acid groups (`-COOH`), one at each end of the molecule. Hence, this amino acid is **acidic**.
- **(iii)**: This structure has only one carboxylic acid group at the end and no additional carboxylic acid in the side chain. Therefore, this amino acid is **not acidic**.
- **(iv)**: This structure has two carboxylic acid groups (`-COOH`), one at each end of the molecule. Hence, this amino acid is **acidic**.

3. **Conclusion**:
- The acidic amino acids from the options provided are **(ii)** and **(iv)**.

### Final Answer:
The acidic amino acids are (ii) `HOOC-CH2-CH2-NH2-COOH` and (iv) `HOOC-CH(NH2)-COOH`.

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