What are the two forms of oxygen found in the atmosphere?

"Forests influence the quality of our air, soil and water resources." Justify the statement.

Define green revolution. What are the common objectives of crop improvement?

When an incense stick (agarbatti) is lighted in one corner of a room, its fragrance quickly spreads in the entire room. Name the process involved in this. 

A girl is cooking some food in the kitchen. The smell of food being cooked soon reaches her brother’s room. Explain how the smell could have reached her brother’s room.

Hydrogen has three isotopes written as : ${}_1{}^1\mathrm{H}, {}_1{}^2\mathrm{H}, {}_1{}^3\mathrm{H}$

Explain why these Isotopes have almost identical chemical properties.