The correct option is 2 and 3 only because copper smelting plants pose environmental concerns primarily through the release of pollutants like sulfur dioxide, which can lead to acid rain and respiratory issues, and the potential leaching of heavy metals from copper slag, which can contaminate soil and water, posing risks to ecosystems and human health. These factors underline the need for stringent environmental regulations and pollution control measures in industrial operations, emphasizing sustainable practices to mitigate adverse environmental impacts, aligned with the principles of industrial ecology and environmental management as often discussed in UPSC-preparatory materials.