Increasing order of boiling points of the following
`CH_3CHO`
`CH_3CH_2OH`
`CH_3OCH_3`
`CH_3CH_2CH_3`

Options

A. `I lt II lt III lt IV`
B. `IV lt III lt II lt I`
C. `IV lt III lt I lt II`
D. `II lt I lt III lt IV`

Answer

To determine the increasing order of boiling points for the compounds CH₃CHO (acetaldehyde), CH₃CH₂OH (ethanol), CH₃OCH₃ (dimethyl ether), and CH₃CH₂CH₃ (propane), we need to analyze the types of intermolecular forces present in each compound.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- CH₃CHO: Acetaldehyde (an aldehyde)
- CH₃CH₂OH: Ethanol (an alcohol)
- CH₃OCH₃: Dimethyl ether (an ether)
- CH₃CH₂CH₃: Propane (an alkane)

2. **Analyze Intermolecular Forces:**
- **Ethanol (CH₃CH₂OH)**: This compound can form hydrogen bonds due to the presence of the hydroxyl (-OH) group. Hydrogen bonding is a strong type of intermolecular force, which leads to a higher boiling point.
- **Acetaldehyde (CH₃CHO)**: This compound has a polar carbonyl (C=O) group, which allows for dipole-dipole interactions. However, it cannot form hydrogen bonds as effectively as alcohols.
- **Dimethyl ether (CH₃OCH₃)**: This compound can also engage in dipole-dipole interactions due to the polar C-O bond, but it lacks hydrogen bonding capabilities, making its boiling point lower than that of alcohols.
- **Propane (CH₃CH₂CH₃)**: This is a non-polar molecule that primarily exhibits London dispersion forces, which are the weakest type of intermolecular force. Therefore, it has the lowest boiling point among the four.

3. **Rank the Compounds by Boiling Point:**
- The strongest intermolecular forces will lead to the highest boiling point. Therefore, we rank the compounds as follows:
- **Lowest Boiling Point**: Propane (CH₃CH₂CH₃) - London dispersion forces
- **Next**: Dimethyl ether (CH₃OCH₃) - Dipole-dipole interactions
- **Next**: Acetaldehyde (CH₃CHO) - Dipole-dipole interactions
- **Highest Boiling Point**: Ethanol (CH₃CH₂OH) - Hydrogen bonding

4. **Final Order:**
- The increasing order of boiling points is:
- CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CHO < CH₃CH₂OH

### Final Answer:
**Increasing order of boiling points:** CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CHO < CH₃CH₂OH