He is majoring in chemistry at university.

This chemical reacts when heat is added.

This chemical reaction is very dangerous.

He is an expert in chemistry.

He received the letter challenging him to a duel and began preparing for the duel.

Gender roles are an important element in defining individual behavior in society.

His role is to fulfill his responsibilities as a leader.

Transition metals play an important role in chemical reactions.

It is important to understand the importance of health.

Understanding the transition state of a chemical reaction is important for predicting the progress of the reaction.