Case: Read the passage and answer the question.
The nucleus of an atom is a dense central 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 very small as compared to that of an atom.
Which of the following is true?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The nucleus is a heavy mass at the centre of the atom.
The passage says that the nucleus is a dense central mass of protons and neutrons. It also says that the nucleus is very small compared with the atom, so an atom is almost empty.
Option (1) The volume of a neutron is about \( 10^{12} \) times the volume of an atom. — Incorrect. A neutron lies inside the nucleus. If the atom were the size of a classroom, the nucleus would be only a pinhead. So a neutron takes up a tiny part of the volume of the atom. It cannot be \( 10^{12} \) times larger than the atom.
Option (2) The part of the atom outside the nucleus is massive. — Incorrect. Outside the nucleus there are only the light electrons. Nearly all the mass of the atom is in the nucleus, so the part outside the nucleus is not massive.
Option (3) The nucleus is a heavy mass at the centre of the atom. — Correct. The passage calls the nucleus a dense central mass, so it is a heavy mass at the centre of the atom. Nearly all the mass of the atom sits in this tiny nucleus.