The correct option for the formation of ethene from the dehydration of ethanol is **B. an elimination reaction**. ### Detailed Explanation: 1. **Understanding Dehydration of Ethanol**: - The dehydration of ethanol (C₂H₅OH) involves the removal of a water molecule (H₂O) from the ethanol molecule. This process can be represented by the following chemical equation: \[ C_2H_5OH \rightarrow C_2H_4 + H_2O \] - In this reaction, ethanol is converted into ethene (C₂H₄) and water. 2. **What is an Elimination Reaction?**: - An elimination reaction is a type of chemical reaction where two substituents are removed from a molecule, resulting in the formation of a double bond or a ring structure. In the case of ethanol, the removal of a hydroxyl group (-OH) and a hydrogen atom (H) leads to the formation of a double bond between the two carbon atoms, resulting in ethene. - The general form of an elimination reaction can be represented as: \[ A-B \rightarrow A + B \] - Here, A and B are groups that are eliminated from the molecule. 3. **Why Option B is Correct**: - In the dehydration of ethanol, the reaction involves the elimination of water (H₂O) from the ethanol molecule. This results in the formation of a double bond between the two carbon atoms, which is characteristic of an elimination reaction. Therefore, the correct classification of this reaction is indeed an elimination reaction. ### Why the Other Options are Incorrect: - **Option A: An Addition Reaction**: - An addition reaction involves the addition of atoms or groups to a molecule without the loss of any atoms. In the case of dehydration, we are not adding anything to ethanol; instead, we are removing components (water). Therefore, this option is incorrect. - **Option C: An Oxidation Reaction**: - Oxidation reactions involve the loss of electrons or an increase in oxidation state, often associated with the addition of oxygen or the removal of hydrogen. The dehydration of ethanol does not fit this definition, as it does not involve a change in oxidation state of the carbon atoms. Thus, this option is also incorrect. - **Option D: A Substitution Reaction**: - A substitution reaction involves the replacement of one atom or group in a molecule with another atom or group. In the dehydration of ethanol, there is no substitution occurring; rather, we are removing parts of the molecule. Therefore, this option is incorrect as well. ### Summary of Key Points: - The dehydration of ethanol to form ethene is classified as an **elimination reaction** because it involves the removal of water and the formation of a double bond. - An elimination reaction results in the loss of two atoms or groups from a molecule, leading to the formation of a new bond. - Other options (addition, oxidation, substitution) do not accurately describe the process occurring in the dehydration of ethanol. ### Revision Summary: - Dehydration of ethanol produces ethene and water. - This process is an **elimination reaction** due to the removal of water. - Other classifications (addition, oxidation, substitution) do not apply to this reaction. - Understanding reaction types is crucial for identifying and classifying chemical processes correctly.