The correct option is **B. Steam methane reforming**. ### Detailed Explanation **What is Steam Methane Reforming (SMR)?** Steam methane reforming is a chemical process used to produce hydrogen from natural gas, which primarily consists of methane (CH₄). In this process, methane reacts with steam (water vapor) at high temperatures (typically between 700°C and 1000°C) in the presence of a catalyst, usually nickel-based. The overall reaction can be summarized as follows: \[ \text{CH}_4 + \text{H}_2\text{O} \rightarrow \text{CO} + 3\text{H}_2 \] This reaction produces carbon monoxide (CO) and hydrogen gas (H₂). The carbon monoxide can further react with steam in a subsequent reaction known as the water-gas shift reaction: \[ \text{CO} + \text{H}_2\text{O} \rightarrow \text{CO}_2 + \text{H}_2 \] This step increases the yield of hydrogen. The final products of the SMR process are hydrogen and carbon dioxide (CO₂). **Why is SMR Important for Ammonia Synthesis?** Hydrogen produced through steam methane reforming is a critical feedstock for the Haber process, which synthesizes ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂): \[ \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \] Ammonia is a key ingredient in fertilizers, which are essential for modern agriculture. Therefore, SMR plays a vital role in both industrial productivity (by providing hydrogen for ammonia production) and environmental sustainability (by enabling the production of fertilizers that can help increase crop yields). ### Why Other Options Are Incorrect **A. Electrolysis** - Electrolysis is a process that uses electricity to split water into hydrogen and oxygen. While it can produce hydrogen, it is not primarily used in the chemical industry for large-scale hydrogen production due to its high energy requirements and cost. It is more commonly used in applications where pure hydrogen is needed or where renewable energy sources are available. **C. Gasification** - Gasification is a process that converts organic or fossil-based materials into carbon monoxide, hydrogen, and carbon dioxide. While it can produce hydrogen, it is typically used for converting coal or biomass into syngas (a mixture of hydrogen and carbon monoxide) rather than natural gas. It is less efficient for hydrogen production compared to SMR when starting from natural gas. **D. Catalytic Cracking** - Catalytic cracking is a refining process used to break down larger hydrocarbon molecules into smaller ones, such as gasoline and diesel. It is not primarily focused on hydrogen production and does not convert natural gas into hydrogen. Instead, it is used to improve the yield of valuable fuels from heavier fractions of crude oil. ### Summary of Key Points - **Steam Methane Reforming (SMR)** is the primary method for converting natural gas into hydrogen for ammonia synthesis. - The process involves reacting methane with steam at high temperatures, producing hydrogen and carbon monoxide. - Hydrogen is essential for the Haber process, which synthesizes ammonia, a key component in fertilizers. - Other methods like electrolysis, gasification, and catalytic cracking are less efficient or not primarily focused on hydrogen production from natural gas. ### Revision Summary - **SMR is the main industrial process for hydrogen production from natural gas.** - **It involves high-temperature reactions with steam and a catalyst.** - **Hydrogen is crucial for ammonia synthesis in fertilizers.** - **Other methods (electrolysis, gasification, catalytic cracking) are less relevant for this purpose.**