Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Electrons in the atom are held by Coulomb forces.
Reason (R): The atom is stable only because the centripetal force due to Coulomb’s law is balanced by the centrifugal force.
Choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A is true but R is false.
Assertion (A) Electrons in the atom are held by Coulomb forces. — True. The negative electrons and the positive nucleus attract each other by Coulomb’s law. This electrostatic attraction keeps each electron bound in its orbit.
Reason (R) The atom is stable only because the centripetal force due to Coulomb’s law is balanced by the centrifugal force. — False. No separate force balances the Coulomb attraction. The attraction itself is the centripetal force that keeps the electron moving in a circle. Such a classical orbit is not even stable, because the accelerated electron would radiate energy and spiral into the nucleus. Bohr had to postulate stable, non-radiating orbits to explain stability.
NCERT (2026-27):
Electron Orbits – “The Rutherford nuclear model of the atom which involves classical concepts, pictures the atom as an electrically neutral sphere consisting of a very small, massive and positively charged nucleus at the centre surrounded by the revolving electrons in their respective dynamically stable orbits. The electrostatic force of attraction, Fe between the revolving electrons and the nucleus provides the requisite centripetal force (Fc) to keep them in their orbits.”
Bohr Model of the Hydrogen Atom – “… According to classical electromagnetic theory, an accelerating charged particle emits radiation in the form of electromagnetic waves. The energy of an accelerating electron should therefore, continuously decrease. The electron would spiral inward and eventually fall into the nucleus …. Thus, such an atom can not be stable.”