Which of the following energy sources is NOT classified as alternative energy?

The answer identifies coal as the energy source that is not classified as alternative energy. Alternative energy refers to sources of energy that are considered more sustainable and environmentally friendly compared to conventional fossil fuels. Wind energy, geothermal energy, and solar energy are all examples of alternative energy sources because they harness natural processes to generate power and typically produce fewer greenhouse gas emissions.

Coal, on the other hand, is a fossil fuel that has been used as a primary energy source for electricity and industrial processes for many years. Its extraction and combustion release significant amounts of carbon dioxide and other pollutants into the atmosphere, contributing to climate change and air quality issues. Due to these negative environmental impacts, coal does not fit the criteria for alternative energy, which aims to reduce reliance on such polluting sources and promote cleaner energy options.