The correct answer is option-4 Biomass energy. Biomass energy is considered a conventional energy source because it has been used for centuries by humans to produce heat and energy. Biomass energy is derived from organic matter such as wood, crop residues, and animal waste. These materials are either burned directly or converted into fuels like ethanol and biodiesel.

Option-1 Tidal energy is not a conventional energy source. Tidal energy is a form of renewable energy that harnesses the natural rise and fall of ocean tides to generate electricity.

Option-2 Geothermal energy is also not a conventional energy source. Geothermal energy is a renewable energy source that utilizes heat from the Earth`s core to generate electricity or provide heating and cooling.

Option-3 Solar energy is a form of renewable energy that uses sunlight to generate electricity. It is not considered a conventional energy source as it relies on the conversion of solar radiation into usable energy.

In conclusion, biomass energy is the only option provided that qualifies as a conventional energy source. Other options are forms of renewable energy.