The correct structure of histidine in a strongly acidic solution `(Ph=2)` is :

Options

A.
B.
C.
D.

Explanation

To determine the correct structure of histidine in a strongly acidic solution (pH = 2), we will follow these steps:

### Step 1: Understand the Structure of Histidine
Histidine is an amino acid with the following general structure:
- A central carbon (C) atom.
- An amino group (-NH2).
- A carboxylic acid group (-COOH).
- A side chain (R group) that contains an imidazole ring.

### Step 2: Draw the Basic Structure of Histidine
The basic structure of histidine can be represented as follows:
- Central carbon connected to:
- An amino group (-NH2).
- A carboxylic acid group (-COOH).
- A side chain (R group) which is an imidazole ring.

### Step 3: Consider the Effect of Strong Acid (pH = 2)
In a strongly acidic solution, the following changes occur:
- The amino group (-NH2) will accept a proton (H+) and become positively charged (-NH3+).
- The carboxylic acid group (-COOH) remains protonated and does not change.

### Step 4: Modify the Structure for Acidic Conditions
Now, we modify the structure based on the acidic conditions:
- The imidazole ring can also be protonated. The nitrogen in the imidazole ring can accept a proton, leading to a positively charged nitrogen.

### Step 5: Final Structure of Histidine in Acidic Medium
The final structure of histidine in a strongly acidic solution will look like this:
- The central carbon is connected to:
- A positively charged amino group (-NH3+).
- A carboxylic acid group (-COOH).
- The imidazole ring where one nitrogen is protonated, resulting in a positively charged imidazole.

### Step 6: Identify the Correct Option
Now, we compare this structure with the given options to identify the correct one. The correct structure will show:
- The carboxylic acid group (-COOH) unaffected.
- The amino group as (-NH3+).
- The imidazole nitrogen as positively charged.

### Conclusion
Based on the above analysis, the correct structure of histidine in a strongly acidic solution (pH = 2) is represented by option A.

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