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

Understanding chemical equilibrium is very important in understanding chemical reactions.

This substance undergoes a chemical change when heat is applied.

In this experiment, you can observe a chemical reaction.

The foundation stone of this building was laid 100 years ago.

The allyl group plays an important role in organic chemistry.

The sulfonyl group plays an important role in chemical reactions.

Free radicals play an important role in chemical reactions.

The phenyl group plays an important role in organic chemistry.

The carbonyl group plays an important role in organic chemistry.