Which gas is added to water to kill bacteria?

What is given out with the exhaled air from the blood?

What do plants get with the help of bacteria in the soil?

What is the process of changing of water or any other liquid to vapour called?

Which is the second layer of the atmosphere?

The purest form of natural water is:

Which is the purest form of water?

What is the first layer above the earth's surface?

After sedimentation, drain the clear water carefully into another beaker .It is called:

Which one of the following is a mixture of gases?