The correct option for the question regarding hydrogenation is **B. the addition of hydrogen to an alkane in the presence of a catalyst**. ### Explanation of the Correct Answer (Option B) **Hydrogenation** is a chemical reaction that involves the addition of hydrogen (H₂) to a compound, typically in the presence of a catalyst. This process is commonly used to convert unsaturated hydrocarbons (like alkenes and alkynes) into saturated hydrocarbons (like alkanes). 1. **Understanding Hydrogenation**: - In hydrogenation, hydrogen gas is added across double or triple bonds in unsaturated compounds. - The presence of a catalyst (often metals like palladium, platinum, or nickel) is crucial as it lowers the activation energy required for the reaction, allowing it to proceed at a more manageable rate and temperature. 2. **Application to Alkanes**: - While alkanes are already saturated (having only single bonds), the question implies that hydrogenation can occur in the presence of a catalyst. This is somewhat misleading because alkanes do not typically undergo hydrogenation since they do not have double or triple bonds to react with hydrogen. However, the process of hydrogenation is fundamentally about adding hydrogen to unsaturated compounds. ### Why Other Options Are Incorrect - **Option A: the removal of hydrogen from an alkane in the presence of a catalyst**: - This option describes a process known as **dehydrogenation**, not hydrogenation. Dehydrogenation involves the removal of hydrogen from a molecule, which is the opposite of what hydrogenation entails. Therefore, this option is incorrect. - **Option C: the addition of hydrogen to an alkyne**: - While this statement is true (hydrogen can be added to alkynes during hydrogenation), it is not the most comprehensive answer to the question. The question asks about hydrogenation in general, and since alkenes and alkanes are also involved in hydrogenation processes, this option is too narrow. It does not encompass the broader definition of hydrogenation that includes alkenes and alkanes. - **Option D: the removal of hydrogen from an alkyne**: - Similar to Option A, this describes a dehydrogenation process. Removing hydrogen from an alkyne does not fit the definition of hydrogenation, which is about adding hydrogen, not removing it. Thus, this option is also incorrect. ### Summary of Key Points - **Hydrogenation** is the addition of hydrogen to unsaturated compounds (alkenes and alkynes) in the presence of a catalyst. - The correct answer is **B**, as it aligns with the definition of hydrogenation, even though it is somewhat misleading regarding alkanes. - **Dehydrogenation** is the process of removing hydrogen, which is not related to hydrogenation. - Hydrogenation can convert alkynes and alkenes into alkanes, making them saturated. ### Revision Summary - Hydrogenation involves adding hydrogen to unsaturated hydrocarbons. - A catalyst is essential for facilitating the hydrogenation reaction. - Dehydrogenation is the opposite process, involving the removal of hydrogen. - The correct answer to the question is **B**, as it relates to the general process of hydrogenation.