Which of the following is a primary fuel source for combustion in power plants?

The primary fuel source for combustion in power plants is fossil fuels such as coal and natural gas. These fuels are widely used due to their energy density and the technology available for their efficient combustion. In a thermal power plant, fossil fuels are burned to generate heat, which in turn produces steam to drive turbines connected to generators. This process is fundamental in converting chemical energy in the fuels into mechanical and then electrical energy.

Coal has been a traditional energy source for decades, while natural gas has gained popularity due to its cleaner-burning properties and efficiency in producing electricity. This combination of factors makes fossil fuels the dominant choice for combustion in many power generation facilities.

Other options like biomass, while a source of energy, are not as prevalent in large-scale power generation compared to fossil fuels. Biomass can be used in some renewable systems but does not provide the same output consistency as fossil fuels. Nuclear energy represents an entirely different process, relying on nuclear fission rather than combustion, and hydropower harnesses kinetic energy from water flow, which does not involve burning a fuel source. Thus, fossil fuels stand out as the primary choice for combustion in power plants.