Which of the following is the major solute species in a solution of alanine at `pH=2` ?

Options

A.
B.
C.
D.

Explanation

To determine the major solute species in a solution of alanine at pH 2, we can follow these steps:

### Step 1: Understand the structure of alanine
Alanine is an amino acid with the following structure:
- It has an amino group (-NH2)
- A carboxyl group (-COOH)
- A side chain (methyl group -CH3)

### Step 2: Identify the pH condition
The given pH is 2, which indicates that the solution is acidic. In an acidic environment, the concentration of hydrogen ions (H⁺) is high.

### Step 3: Analyze the ionization of alanine
At a low pH (acidic conditions), the amino group of alanine can accept a proton (H⁺) due to its basic nature. The carboxyl group (-COOH) can remain protonated as it is already in its acidic form.

### Step 4: Determine the predominant form of alanine
In an acidic solution:
- The amino group will be protonated to form -NH3⁺.
- The carboxyl group will remain as -COOH.

Thus, the predominant form of alanine at pH 2 will be the cationic form, which can be represented as:
- NH3⁺ - CH(CH3) - COOH

### Step 5: Conclusion
The major solute species in a solution of alanine at pH 2 is the protonated form of alanine, which is a cation (NH3⁺ - CH(CH3) - COOH).