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

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

Hydrogen is the most abundant element in the universe.

Transition elements play an important role in chemical reactions.

My grandfather is healthy and living a long life.

Deuterium is one of the isotopes of hydrogen.

I often eat sausage for breakfast.

He is learning the basics of mathematics.

Fundamental knowledge of mathematics is necessary to solve advanced problems.

We decided to establish a new organization.