Pick out the correct statement.

Options

A. Both glycine and p - aminobenzoic acid form dipolar ions
B. Both sulphanilic acid and p - aminobenzoic and form dipolar ions
C. Glycine does not form dipolar ion, but p - aminobenzoic acid forms dipolar ion
D. Both sulphanilic acid and glycine form dipolar ions, but p - aminobenzoic acid does not form dipolar ion

Answer

To solve the question of which statement is correct regarding the formation of dipolar ions by glycine, para-aminobenzoic acid, and sulfanilic acid, we will analyze each option step by step.

### Step 1: Understanding Dipolar Ions
A dipolar ion, also known as a zwitterion, is a molecule that has both positive and negative charges but is overall neutral. This typically occurs in amino acids, which have both an amino group (-NH2) and a carboxyl group (-COOH).

### Step 2: Analyzing Glycine
- Glycine (NH2CH2COOH) is the simplest amino acid.
- It has both an amino group (which can accept a proton) and a carboxyl group (which can donate a proton).
- When glycine is in solution, it can exist as a zwitterion:
- The carboxyl group donates a proton (H+) to become COO⁻.
- The amino group accepts a proton to become NH3⁺.
- Therefore, glycine **does form a dipolar ion**.

### Step 3: Analyzing Para-Aminobenzoic Acid
- Para-aminobenzoic acid (PABA) has a carboxyl group and an amino group attached to a benzene ring.
- The presence of the benzene ring, which is an electron-withdrawing group, affects the ability of the amino group to donate a proton.
- The amino group in PABA cannot effectively accept a proton due to the electron-withdrawing nature of the benzene ring.
- Therefore, para-aminobenzoic acid **does not form a dipolar ion**.

### Step 4: Analyzing Sulfanilic Acid
- Sulfanilic acid contains an amino group (-NH2) and a sulfonic acid group (-SO3H).
- The sulfonic acid group is more acidic than the carboxylic acid group.
- The sulfonic acid can donate a proton, and the amino group can accept a proton.
- Thus, sulfanilic acid can also exist as a zwitterion:
- The sulfonic acid donates a proton to become SO3⁻.
- The amino group accepts a proton to become NH3⁺.
- Therefore, sulfanilic acid **does form a dipolar ion**.

### Step 5: Evaluating the Statements
Now we can evaluate the given statements:
1. **Both glycine and para-aminobenzoic acid form dipolar ions.** (Incorrect, as PABA does not form a dipolar ion)
2. **Both sulfanilic acid and para-aminobenzoic acid form dipolar ions.** (Incorrect, as PABA does not form a dipolar ion)
3. **Glycine does not form dipolar ion but para-aminobenzoic acid forms dipolar ion.** (Incorrect, as glycine does form a dipolar ion)
4. **Both sulfanilic acid and glycine form dipolar ions but para-aminobenzoic acid does not form dipolar ion.** (Correct)

### Conclusion
The correct statement is **Option D**: Both sulfanilic acid and glycine form dipolar ions, but para-aminobenzoic acid does not form a dipolar ion.

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