$A$ modern selenium solar cell can convert $25 \%$ of sunlight into electrical energy.

Which process is used to harness nuclear energy these days? Explain it briefly.

Name the three forms in which energy from oceans is made available for use. What are $OTEC$ power plants? How do they operate?

$(i)$ Distinguish between renewable and non-renewable sources of energy,giving one example of each.
$(ii)$ Why is the use of wood as a fuel not advised,although forests can be replenished?

Which of the following is not a non-renewable source of energy?

Biomass has been used as fuel since ancient times. How has it been modified to function as a more efficient fuel in the recent past?