Which of the following are some important pollutants released by steel industry in India? 1. Oxides of sulphur 2. Oxides of nitrogen 3. Carbon monoxide 4. Carbon dioxide Select the correct answer using the code given below.

The correct answer is (d) because steel production involves high-temperature processes like sintering, coke making, and smelting, which utilize fossil fuels and raw materials that inevitably release $SO_x, NO_x, CO,$ and $CO_2$ as byproducts. Option (a) is the most tempting wrong choice as candidates often overlook $NO_x$, assuming it is primarily a vehicular pollutant, whereas it is actually generated during high-heat industrial combustion when atmospheric nitrogen reacts with oxygen. The core concept tested is the identification of specific emission profiles and environmental footprints associated with major heavy industries.