Arrange the following in decreasing order of their boiling points.
(A). N-butane
(B). 2-methylbutane
(C). N-pentane
(D). 2,2-dimethylpropane

Options

A. `A gt B gt C gt D`
B. `B gt C gt D gt A`
C. `D gt C gt B gt A`
D. `C gt B gt D gt A`

Explanation

To arrange the compounds N-butane, 2-methylbutane, N-pentane, and 2,2-dimethylpropane in decreasing order of their boiling points, we can follow these steps:

### Step 1: Identify the number of carbon atoms in each compound
- **N-butane (A)**: 4 carbon atoms
- **2-methylbutane (B)**: 5 carbon atoms
- **N-pentane (C)**: 5 carbon atoms
- **2,2-dimethylpropane (D)**: 5 carbon atoms

### Step 2: Apply the rule regarding the number of carbon atoms
The boiling point generally increases with an increase in the number of carbon atoms. In this case:
- N-butane has the least number of carbon atoms (4), so it will have the lowest boiling point.

### Step 3: Compare the boiling points of the remaining compounds (B, C, D)
Since B, C, and D all have 5 carbon atoms, we need to consider the branching:
- **N-pentane (C)**: Straight-chain, no branching.
- **2-methylbutane (B)**: One branch.
- **2,2-dimethylpropane (D)**: Two branches.

### Step 4: Apply the rule regarding branching
More branching results in a lower boiling point due to decreased surface area:
- **N-pentane (C)**: No branching, highest boiling point among B, C, and D.
- **2-methylbutane (B)**: One branch, higher boiling point than D.
- **2,2-dimethylpropane (D)**: More branching, lowest boiling point among B, C, and D.

### Step 5: Arrange the compounds in decreasing order of boiling points
Based on the analysis:
1. N-pentane (C) - highest boiling point
2. 2-methylbutane (B)
3. 2,2-dimethylpropane (D)
4. N-butane (A) - lowest boiling point

### Final Order:
The final order of boiling points from highest to lowest is:
**C > B > D > A**