Read the passage and answer the question.

Nucleus of an atom is central dense mass consisting of protons and neutrons. If an atom is enlarged to the size of a classroom, the nucleus would be the size of a pinhead. In other words, an atom is almost empty. The size of a nucleus is that as compared to that of an atom.

Which of the following is true?

Nucleus is a heavy mass at the center.

It's the nucleus that is a dense mass and contains most of the mass of the atom.