The boiling point of a compound depends on various factors such as molecular weight, type of bonding, and intermolecular forces. In this case, let’s analyze the given options: Option (1) CH$_3$CH$_2$CH$_2$CH$_3$ (Butane): This is a hydrocarbon with weak Van der Waals forces. It has a relatively low boiling point due to the absence of hydrogen bonding. Option (2) CH$_3$CH$_2$CH$_2$CH$_2$OH (Butanol): This compound contains an --OH (hydroxyl) group, which allows for hydrogen bonding between molecules. Hydrogen bonding significantly increases the boiling point compared to compounds with only Van der Waals interactions. Option (3) CH$_3$CH$_2$CH$_2$CHO (Butanal): This compound has a carbonyl group (C=O), leading to dipole-dipole interactions. However, these interactions are weaker than the hydrogen bonding present in alcohols. Option (4) C$_2$H$_5$OC$_2$H$_5$ (Diethyl ether): This compound contains an ether linkage, resulting in weak dipole-dipole interactions, but it lacks hydrogen bonding. Conclusion: Among the given compounds, CH$_3$CH$_2$CH$_2$CH$_2$OH (butanol) has the highest boiling point due to the presence of strong intermolecular hydrogen bonding.
