Layer of atmosphere which is fit for respiration.

Who discovered oxygen gas by heating mercury II oxide in a hard glass test tube.

Air is a mixture whose composition varies at different-intervals of time and places.

What is the volume of oxygen in the atmosphere.

The product of photosynthesis is ____________ [glucose] which is the food manufactured-by the plants.

A natural process by which green plants manufacture food in the presence of sunlight.

Choose the correct chemical formula of limestone.

Which gas initiates acid rainfall.

Choose the correct chemical formula of phosphorus pentoxide