Which one among the following is a non-conventional source of energy?

Which one among the following is a non-conventional source of energy?

Petroleum
Coal
Radioactive elements
Solar energy
This question was previously asked in
UPSC CDS-2 – 2020
Solar energy is considered a non-conventional or renewable source of energy.
Conventional energy sources are typically fossil fuels (coal, petroleum, natural gas) and nuclear energy, which are finite or use processes developed conventionally. Non-conventional sources are renewable and environmentally friendly, such as solar, wind, geothermal, tidal, and biomass energy.
Radioactive elements are used in nuclear power plants, which is often categorised as a conventional source due to its established technology and non-renewable fuel source (uranium).