Arrange the following compounds in increasing order of their boiling points `CH_3CHO ,CH_3CH_2OH ,CH_3OCH_3,CH_3CH_2CH_3`

Options

A. `CH_3CH_2CH_3 lt CH_3CH_2OH ltCH_3OCH_3lt CH_3CHO`
B. `CH_3OCH_3lt CH_3CH_2CH_3ltCH_3CH_2OH ltCH_3CHO`
C. `CH_3CH_2CH_3lt CH_3OCH_3lt CH_3CHOlt CH_3CH_2OH`
D. `CH_3OCH_3lt CH_3CH_2CH_3ltCH_3CH_2OH ltCH_3CHO`

Answer

To arrange the compounds `CH_3CHO` (acetaldehyde), `CH_3CH_2OH` (ethanol), `CH_3OCH_3` (dimethyl ether), and `CH_3CH_2CH_3` (propane) in increasing order of their boiling points, we need to consider the types of intermolecular forces present in each compound.

### Step-by-Step Solution:

1. **Identify the Compounds and Their Functional Groups:**
- `CH_3CHO`: This is acetaldehyde, which is an aldehyde.
- `CH_3CH_2OH`: This is ethanol, which is an alcohol.
- `CH_3OCH_3`: This is dimethyl ether, which is an ether.
- `CH_3CH_2CH_3`: This is propane, which is an alkane.

2. **Determine the Intermolecular Forces:**
- **Ethanol (`CH_3CH_2OH`)**: Alcohols can form hydrogen bonds due to the presence of the hydroxyl (-OH) group. Hydrogen bonding is a strong intermolecular force, leading to a higher boiling point.
- **Acetaldehyde (`CH_3CHO`)**: Aldehydes can also exhibit dipole-dipole interactions due to the polar carbonyl (C=O) group, but they do not form hydrogen bonds. Therefore, their boiling point is lower than that of alcohols but higher than that of ethers and alkanes.
- **Dimethyl Ether (`CH_3OCH_3`)**: Ethers can also engage in dipole-dipole interactions because of the polar C-O bond, but they do not have hydrogen bonding. Thus, their boiling point is lower than that of alcohols and higher than that of alkanes.
- **Propane (`CH_3CH_2CH_3`)**: Alkanes primarily exhibit London dispersion forces, which are the weakest intermolecular forces. Therefore, propane will have the lowest boiling point among the four compounds.

3. **Rank the Compounds by Boiling Points:**
- **Lowest Boiling Point**: Propane (`CH_3CH_2CH_3`) - London dispersion forces.
- **Next**: Dimethyl Ether (`CH_3OCH_3`) - Dipole-dipole interactions.
- **Next**: Acetaldehyde (`CH_3CHO`) - Dipole-dipole interactions.
- **Highest Boiling Point**: Ethanol (`CH_3CH_2OH`) - Hydrogen bonding.

### Final Order of Boiling Points:
`CH_3CH_2CH_3 < CH_3OCH_3 < CH_3CHO < CH_3CH_2OH`