The industrial activity held least responsible for global warming is :

Question: Which industrial activity is least responsible for global warming?

Option 1: Cement manufacturing.

Cement production involves heating limestone ($$CaCO_3$$), which releases large amounts of $$CO_2$$: $$CaCO_3 \rightarrow CaO + CO_2$$. The cement industry accounts for about 8% of global $$CO_2$$ emissions. Major contributor to global warming.

Option 2: Steel manufacturing.

Steel production uses coke (carbon) to reduce iron ore, releasing significant $$CO_2$$. It is one of the largest industrial sources of greenhouse gases. Major contributor.

Option 3: Electricity generation in thermal power plants.

Burning fossil fuels (coal, natural gas) in thermal power plants is the single largest source of $$CO_2$$ emissions globally. Largest contributor.

Option 4: Industrial production of urea.

Urea production involves the reaction: $$2NH_3 + CO_2 \rightarrow NH_2CONH_2 + H_2O$$. This process actually consumes CO₂ as a raw material. While some energy is used, the process itself absorbs carbon dioxide, making it the least responsible for global warming among the given options.

The correct answer is Option 4.