The boiling point of a substance is dependent on the strength of the intermolecular forces between its molecules. Stronger intermolecular forces require more energy to overcome, thus resulting in a higher boiling point.

In the case of butan-1-ol and ethoxyethane (diethyl ether), they are both composed of similar numbers of similar atoms, but the type of intermolecular force between the molecules differs due to their functional groups.

Butan-1-ol is an alcohol and has a -OH group, which allows for hydrogen bonding, a strong type of dipole-dipole interaction. This happens when the hydrogen atom in a polar bond (especially -OH, -NH, -HF) is attracted to some electronegative atom (like O, N, or F) in another molecule. Because of this, butan-1-ol molecules "stick together" more strongly, requiring more heat energy to separate them and thus exhibiting a higher boiling point.

On the other hand, ethoxyethane, being an ether, does not have the ability to form hydrogen bonds since it lacks the -OH group. The primary intermolecular forces in ethers are relatively weaker van der Waals forces. Therefore, it requires less heat energy to break these forces, resulting in a lower boiling point compared to butan-1-ol.

So, both A and R are true and R is indeed the correct explanation for A.