(a) What are fossil fuels? Give three examples of fossil fuels.
(b) Describe how fossil fuels were formed.
(c) Explain how, sun is considered to be the ultimate source of fossil fuels.
(d) Which fossil fuels were formed by the buried remains of small plants and animals?
(e) Which fossil fuel formed by the buried remains of large land plants?

(a) Fossil fuels are the natural fuels that are found deep inside the earth and are formed from the prehistoric remains of the organisms.

Three examples of fossil fuels are coal, petroleum and natural gas.

(b) The plants and animals which died millions of years ago got buried deep inside the earth, in the absence of oxygen got converted into fossil fuels such as coal, petroleum and natural gas, due to the chemical effects of bacteria along with continuous pressure and heat. The buried remains of large plants get converted into coal and the remains of small plants and animals into petroleum and natural gas.

(c) We know that green plants use sunlight for photosynthesis, which is the process by which they make food for their growth. When the plants are eaten by the animals, they consume food made with the help of sunlight. When these plants and animals die, their remains, which consist of material directly or indirectly made with the help of sunlight, are get buried in the earth and converted into fossil fuels, such as coal and petroleum.

Thus, the sun is the ultimate source of fossil fuels.

(d) Petroleum and natural gas were formed by the buried remains of small plants and animals.

(e) Coal is formed from by the buried remains of large land plants.