The correct order of decreasing boiling points of `CH_(3)CONH_(2) (A), CH_(3)`COCl (B), `CH_(3)`COOH (C ) and `(CH_(3)CO)_(2)`O (D ) is

Options

A. `A gt D gt C gt B `
B. `A gt B gt C gt D `
C. `D gt C gt B gt A `
D. None of these

Explanation

To determine the correct order of decreasing boiling points of the compounds \( CH_3CONH_2 \) (Acetamide, A), \( CH_3COCl \) (Acetyl Chloride, B), \( CH_3COOH \) (Acetic Acid, C), and \( (CH_3CO)_2O \) (Acetic Anhydride, D), we need to analyze the molecular structure and the types of intermolecular forces present in each compound.

### Step 1: Analyze Acetamide (\( CH_3CONH_2 \))
Acetamide has a carbonyl group (C=O) and an amine group (NH2). The presence of the NH2 group allows for hydrogen bonding, which is a strong intermolecular force. The ability to form multiple hydrogen bonds increases the molecular association, leading to a higher boiling point.

**Hint:** Look for the presence of hydrogen bonding in the structure.

### Step 2: Analyze Acetyl Chloride (\( CH_3COCl \))
Acetyl chloride has a carbonyl group but does not have an active hydrogen atom capable of forming hydrogen bonds. Therefore, it primarily relies on dipole-dipole interactions, which are weaker than hydrogen bonds.

**Hint:** Identify the presence or absence of active hydrogen for hydrogen bonding.

### Step 3: Analyze Acetic Acid (\( CH_3COOH \))
Acetic acid can form hydrogen bonds due to the presence of the hydroxyl group (–OH). However, the molecular association is less than that of acetamide because acetic acid primarily forms dimers (two molecules interacting) rather than extensive networks.

**Hint:** Consider how many molecules can interact through hydrogen bonding.

### Step 4: Analyze Acetic Anhydride (\( (CH_3CO)_2O \))
Acetic anhydride has a larger molecular size compared to acetic acid and can also exhibit dipole-dipole interactions. However, it lacks active hydrogen atoms, which means it cannot form hydrogen bonds like acetamide and acetic acid.

**Hint:** Compare the molecular size and the types of intermolecular forces.

### Step 5: Compare the Boiling Points
1. **Acetamide (A)**: Highest boiling point due to strong hydrogen bonding and high molecular association.
2. **Acetic Anhydride (D)**: Next highest due to larger molecular size and dipole-dipole interactions, but no hydrogen bonding.
3. **Acetic Acid (C)**: Lower than acetic anhydride due to fewer hydrogen bonds (dimer formation).
4. **Acetyl Chloride (B)**: Lowest boiling point due to absence of hydrogen bonding and weaker dipole-dipole interactions.

### Conclusion
The correct order of decreasing boiling points is:
\[ CH_3CONH_2 (A) > (CH_3CO)_2O (D) > CH_3COOH (C) > CH_3COCl (B) \]

### Final Answer
**Order of decreasing boiling points:** \( A > D > C > B \)