Why is there a concern about copper smelting plants?
1. They may release lethal quantities of carbon monoxide into environment.
2. The copper slag can cause the leaching of some heavy metals into environment.
3. They may release sulphur dioxide as a pollutant.
Select the correct answer using the code given below.

Correct Option: 2 and 3 only

Statement 1 is incorrect because copper smelting plants primarily emit sulphur dioxide and particulate matter, not lethal quantities of carbon monoxide. Statement 2 is correct because copper slag contains heavy metals like copper, lead, zinc, and iron, which can leach into soil and groundwater if improperly managed. Statement 3 is correct as sulphur dioxide ($ ext{SO}_2$) gas is a major pollutant emitted during the smelting of sulphide copper ores, posing severe air quality and acid rain concerns.