A newly planted sapling usually grows and matures into a tree in more than:
A. 50 years

B. 25 years

C. 45 years

D. 15 years

Why do we need alternative sources of energy?

Biogas is considered to be a boon to the farmers. Give reasons.

The calorific values of three fuels A, B and C are 33 KJ/g, 150 KJ/g, respectively. A is solid, B is liquid and C is a gas at room temperature. On combustion, both A and B produces carbon dioxide while C explodes forming steam. B and C leave no residue after combustion while A leaves behind some solid residue. Which one of the three fuels is the most ideal? Give two reasons to support your answer.

Calorific value and ignition temperature of fuel X are 75 kJ/g and 200C respectively. These values for fuel Y are 50 kJ/g and 750C respectively. On burning, the fuel Y produces only CO₂ while fuel X produces CO₂ and CO. Which of the two is a better fuel? Give two reasons to support your answer.

Most of the fuels contain carbon as one of the constituents. Name a fuel which has very high calorific value but does not contain carbon.

List two practical uses of bio-gas in rural areas.

Which one of the following is not renewable energy technology?

Which of the following is more environment friendly ?