Photosynthesis is a process in which plants:

1. take in oxygen and give out carbon dioxide
2. take in carbon dioxide and give out oxygen
3. take in nitrogen and give out oxygen.
4. none of the above

Fuels which do not leave any residue on burning are:

1. coal and wood
2. coal and LPG
3. wood and CNG
4. LPG and CNG.

Which of the following is common in combustion and respiration ?

1. oxygen
2. release of heat and light
3. natural process
4. nitrogen.

Which of the gas present in air is required for the synthesis of proteins in plants ?

1. Oxygen
2. Nitrogen
3. Ozone
4. Carbon dioxide