An amino acid is characterized by two pKa values the one corresponding to the more acidic site is designated as `pKa_1` and the other corresponding to the less acidic site is designated as `pKa_2` The isoelectric point also called isoionic point (pI) is the pH at which concentration of zwitter ion is maximum . pI is the average of `pKa_1` and `pKa_2`.Generally the value of pI is slightly less than 7.
some amino acids have side chain with acidic or basic groups.These amino acids have `pKa_3` value also for the side chain.Acidic amino acid have acidic side chains and basic amino acids have basic side chains . pI for acidic amino acid is average of `pKa_1 and pKa_3`.pI for basic amino acid is the average of `pKa_2 and pKa_3`.
`{:(S.NO,"Amino acid",p^(Ka1),p^(Ka2),p^(Ka3)("side chain")),(I,"Aspartic acid",1.88,9.6,3.65),(II,"Glutamic acid",2.19,9.67,4.25),(III,"Lysine",2.18,8.95,10.53),(IV,"Arginine",2.17,9.04,12.48):}`
In the table given above the acidic amino acids are

Options

A. I,II
B. I,III
C. II,III
D. I,II, IV

Explanation

To determine which amino acids from the given table are acidic, we need to analyze the provided pKa values for each amino acid, particularly focusing on the pKa3 values (the side chain pKa values). Acidic amino acids will have lower pKa3 values, indicating that they have acidic side chains.

### Step-by-Step Solution:

1. **Identify the pKa values for each amino acid:**
- Aspartic acid: pKa1 = 1.88, pKa2 = 9.6, pKa3 = 3.65
- Glutamic acid: pKa1 = 2.19, pKa2 = 9.67, pKa3 = 4.25
- Lysine: pKa1 = 2.18, pKa2 = 8.95, pKa3 = 10.53
- Arginine: pKa1 = 2.17, pKa2 = 9.04, pKa3 = 12.48

2. **Determine the nature of the side chains:**
- For aspartic acid, the pKa3 value is 3.65, which is relatively low, indicating it is an acidic side chain.
- For glutamic acid, the pKa3 value is 4.25, which is also low, indicating it is an acidic side chain.
- For lysine, the pKa3 value is 10.53, which is high, indicating it has a basic side chain.
- For arginine, the pKa3 value is 12.48, which is also high, indicating it has a basic side chain.

3. **Identify the acidic amino acids:**
- Based on the analysis, aspartic acid and glutamic acid have low pKa3 values, confirming that they are acidic amino acids.
- Lysine and arginine do not qualify as acidic amino acids due to their high pKa3 values.

4. **Conclusion:**
- The acidic amino acids from the table are **Aspartic acid and Glutamic acid**.

### Final Answer:
The acidic amino acids are **Aspartic acid (I)** and **Glutamic acid (II)**.

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