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 for the nucleus?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → It attracts negative charges.
Option (1) It is electrically neutral as it contains neutrons. — Incorrect. The neutrons carry no charge, but the protons do. So the nucleus has a charge \( +Ze \) and is positively charged.
Option (2) It is held together by gravitational forces as it has mass. — Incorrect. Gravity between nucleons is far too weak. The nucleons are held together by the nuclear force, which is much stronger than both the Coulomb and the gravitational forces.
Option (3) It attracts negative charges. — Correct. The nucleus carries the positive charge of its protons, so it attracts negative charges by the Coulomb force. This attraction keeps the electrons of the atom around it.
Option (4) It is very light as compared to an electron. — Incorrect. The nucleus holds more than 99.9% of the mass of the atom. Even a single proton (1.00727 u) is much heavier than an electron (0.00055 u).
NCERT (2026-27):
Introduction – “In the previous chapter, we have learnt that in every atom, the positive charge and mass are densely concentrated at the centre of the atom forming its nucleus.”