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

1. Carbon monoxide: Copper smelters are mainly associated with sulphur dioxide (SO2) emissions from sulphide ores, not with release of lethal quantities of carbon monoxide as the core concern. Verdict: Incorrect.

2. Copper slag: Copper slag can contain heavy metals and may lead to leaching into soil/water if improperly handled or dumped. Verdict: Correct.

3. Sulphur dioxide: Smelting of copper sulphide ores can release significant SO2, a major air pollutant and key environmental concern. Verdict: Correct.

Hence, 2 and 3 only are correct.