the acidic group in aqueous solution of glycine is

Options

A. `-COOH`
B. `-COO^(-)`
C. `-NH_2`
D. `-NH_3^(+)`

Answer

To determine the acidic group in the aqueous solution of glycine, we can follow these steps:

### Step 1: Understand the Structure of Glycine
Glycine is the simplest amino acid with the chemical formula NH2CH2COOH. It contains an amino group (-NH2) and a carboxylic acid group (-COOH).

### Step 2: Identify the Functional Groups
In glycine, the two functional groups are:
- The amino group (-NH2), which can act as a base.
- The carboxylic acid group (-COOH), which can act as an acid.

### Step 3: Determine the Behavior in Aqueous Solution
In an aqueous solution, glycine can exist in a zwitterionic form, where the carboxylic acid group donates a proton (H+) to the amino group. This results in the formation of a dipolar ion (zwitterion).

### Step 4: Formation of the Zwitterion
The zwitterion of glycine can be represented as:
- The carboxylate ion (COO-) carries a negative charge.
- The ammonium ion (NH3+) carries a positive charge.

### Step 5: Identify the Acidic Group
The acidic character in this zwitterionic form is attributed to the ammonium ion (NH3+). This is because it can release a proton, making it behave like an acid.

### Conclusion
Thus, the acidic group in the aqueous solution of glycine is the ammonium ion (NH3+).

### Final Answer
The acidic group in aqueous solution of glycine is **NH3+**.

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