Answer: Coal
Explanation: Coal is very extensively used in many places. Coal is a non renewable source of energy which means that they cannot be regenerated again.
Due to the extensive use of coal, it produced a huge amount of sulfur content into the atmosphere, similar to the sulfur that releases into the atmosphere through volcanic eruptions. This sulfur then gets mix up with the atmospheric oxygen, forming sulfur dioxide. Due to this reaction, often acid rain occurs at various places. This increasing content of sulfur dioxide is responsible for the global rise in the temperature, thereby causing significant amount of pollution.
Thus, coal burning is the most polluting energy source.
