Oxygen, which is one of the chemical elements, is necessary for us to breathe.

This chemical reaction is very dangerous.

There is a possibility that an earthquake may happen.

Hydrogen is the most abundant element in the universe.

This chemical reaction occurs by the synthesis of two elements.

He is conducting an experiment to synthesize a new compound.

She had two apples.

This chemical reaction is very dangerous.

This chemical reacts when heat is added.

He is majoring in chemistry at university.