How tall is this building?

This chemical reacts when heat is added.

This chemical reaction is very dangerous.

He is an expert in chemistry.

This is my first question.

Rare earth elements are essential materials for the manufacture of electronic devices.

An isotope refers to elements with the same atomic number but different numbers of neutrons.

Transition elements play an important role in chemical reactions.

He has a discerning eye, so he always chooses the highest quality wine.

Because he has discerning taste, he always chooses the best items.