What is the most important characteristic of a good fuel?

Increasing demand for fossil fuels has caused harm to our environment. List its three ill-effects. Suggest three measures to reduce the consumption of fossil fuels.

Which of the following sources of energy is different from the other?

Why is there a need to harness non-conventional sources of energy? Give two main reasons.

$(i)$ 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?

State whether the following statement is true or false:
Spherical reflectors are used to obtain high temperatures in solar heating devices.