The correct option is **B. Cement production**. ### Detailed Explanation Cement production is one of the most significant industrial processes that releases carbon dioxide (CO₂) as a byproduct, contributing to environmental concerns related to climate change. Here’s a step-by-step breakdown of why this is the case: 1. **Cement Composition and Production**: - Cement is primarily made from limestone (calcium carbonate, CaCO₃) and clay. The production process involves heating limestone in a kiln to produce lime (calcium oxide, CaO) and CO₂. - The chemical reaction can be represented as: \[ \text{CaCO}_3 \, (s) \rightarrow \text{CaO} \, (s) + \text{CO}_2 \, (g) \] - For every ton of cement produced, approximately 0.5 tons of CO₂ are released into the atmosphere. 2. **Scale of Production**: - Cement is one of the most widely used construction materials globally. The sheer volume of cement produced (over 4 billion tons annually) means that the total CO₂ emissions from this process are substantial. - The cement industry is estimated to contribute about 8% of global CO₂ emissions, making it a significant contributor to climate change. 3. **Environmental Impact**: - The CO₂ released during cement production contributes to the greenhouse effect, which is a major driver of global warming and climate change. - Efforts to reduce emissions from cement production include using alternative materials, improving energy efficiency, and capturing CO₂ emissions. ### Analysis of Other Options **A. Ammonia synthesis**: - While ammonia synthesis (Haber process) does produce CO₂, it is primarily associated with the use of natural gas as a feedstock. The process itself is not as significant in terms of CO₂ emissions compared to cement production. The overall contribution to global emissions is lower than that of cement. **C. Paper manufacturing**: - Paper manufacturing does involve some CO₂ emissions, primarily from the energy used in the process and the decomposition of organic materials. However, it is not a major contributor to global CO₂ emissions compared to cement production. **D. Water purification**: - Water purification processes can involve chemical treatments that may produce some CO₂, but these processes are generally not associated with significant CO₂ emissions. The environmental impact of water purification is more related to energy consumption and chemical use rather than direct CO₂ emissions. ### Summary of Key Points - **Cement production** is the largest industrial source of CO₂ emissions, contributing about 8% of global emissions. - The process involves the thermal decomposition of limestone, releasing CO₂ as a byproduct. - Other options like ammonia synthesis, paper manufacturing, and water purification contribute less significantly to CO₂ emissions. - Efforts to mitigate emissions from cement production are crucial for addressing climate change. ### Revision Summary - Cement production is the largest industrial source of CO₂ emissions. - The reaction of limestone in cement production releases significant amounts of CO₂. - Other industrial processes contribute less to CO₂ emissions compared to cement. - Understanding the environmental impact of these processes is essential for climate change mitigation efforts.