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.

Organic solvents play an important role in chemical reactions.

It is important to understand the importance of health.

This reaction occurs through a chemical process.

He is an excellent chemist who made many discoveries.

He is an expert in petrochemistry.

It's difficult to decipher this chemical equation.