Arrange the following compounds in decreasing order of their boiling points. (i) `CH_3Br`
`CH_3CH_2Br`
`CH_3CH_2CH_2Br`
`CH3CH_2CH_2CH_2Br`

Options

A. (i)>(ii)>(iii)>(iv)
B. (iv)>(iii)>(ii)>(i)
C. (i)gt(iii)gt(ii)gt(iv)
D. (iii)gt(iv)gt(i)gt(ii)

Answer

To arrange the compounds `CH3Br`, `CH3CH2Br`, `CH3CH2CH2Br`, and `CH3CH2CH2CH2Br` in decreasing order of their boiling points, we can follow these steps:

### Step 1: Understand the factors affecting boiling points
Boiling points of organic compounds are influenced by several factors, including molecular weight (molar mass), intermolecular forces (such as dipole-dipole interactions and van der Waals forces), and the structure of the molecules. Generally, higher molar mass leads to higher boiling points due to increased van der Waals forces.

### Step 2: Determine the molar mass of each compound
1. **`CH3Br`**:
- Molar mass = 12 (C) + 3(1) (H) + 80 (Br) = 12 + 3 + 80 = 95 g/mol
2. **`CH3CH2Br`**:
- Molar mass = 12(2) + 5(1) + 80 (Br) = 24 + 5 + 80 = 109 g/mol
3. **`CH3CH2CH2Br`**:
- Molar mass = 12(3) + 8(1) + 80 (Br) = 36 + 8 + 80 = 124 g/mol
4. **`CH3CH2CH2CH2Br`**:
- Molar mass = 12(4) + 10(1) + 80 (Br) = 48 + 10 + 80 = 138 g/mol

### Step 3: Compare the molar masses
Now we can compare the molar masses:
- `CH3Br`: 95 g/mol
- `CH3CH2Br`: 109 g/mol
- `CH3CH2CH2Br`: 124 g/mol
- `CH3CH2CH2CH2Br`: 138 g/mol

### Step 4: Arrange the compounds in order of boiling points
Since boiling points increase with increasing molar mass, we can arrange the compounds in decreasing order of their boiling points:
1. **`CH3CH2CH2CH2Br`** (highest molar mass, highest boiling point)
2. **`CH3CH2CH2Br`**
3. **`CH3CH2Br`**
4. **`CH3Br`** (lowest molar mass, lowest boiling point)

### Final Answer
The order of the compounds in decreasing order of their boiling points is:
`CH3CH2CH2CH2Br > CH3CH2CH2Br > CH3CH2Br > CH3Br`