Final answer:
An alcohol can be dehydrated to form an alkene when subjected to high temperature and excess acid. Ethers can also be produced through dehydration but under different conditions. Aldehydes and ketones are the products of oxidation, not dehydration, of alcohols.
Step-by-step explanation:
The product that would be made from an alcohol by a dehydration reaction is an alkene. Dehydration is a chemical reaction that involves the removal of a water molecule from a substance. When an alcohol undergoes dehydration, in the presence of a catalyst and at higher temperature with excess acid, the reaction removes the OH group from the alcohol carbon atom and a hydrogen atom from an adjacent carbon atom, resulting in the formation of an alkene and water. This process is distinct from oxidation, which converts primary alcohols into aldehydes and secondary alcohols into ketones.
In some cases, alcohols can also be dehydrated to form ethers, particularly when the reaction occurs at a lower temperature and with an excess of alcohol. However, this process differs from the formation of alkenes and is not the primary focus in the context of the given question.