Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): If the total energy of the electron in a hydrogen atom is negative, the electron is bound to the nucleus.
Reason (R): The Bohr model is valid for both one-electron atoms and multi-electron atoms.
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) If the total energy of the electron in a hydrogen atom is negative, the electron is bound to the nucleus. — True. The total energy of the orbiting electron is \( E=-e^2/8\pi\varepsilon_0 r \). A negative energy means that energy must be supplied to take the electron infinitely far from the nucleus. So the electron is bound. With a positive energy it would not follow a closed orbit.
Reason (R) The Bohr model is valid for both one-electron atoms and multi-electron atoms. — False. The Bohr model applies only to hydrogenic (single-electron) atoms. It cannot be extended even to helium. There, each electron interacts with the nucleus and also with all the other electrons. The model includes only the electron–nucleus force.
NCERT (2026-27):
Electron Orbits – “The total energy of the electron is negative. This implies the fact that the electron is bound to the nucleus. If E were positive, an electron will not follow a closed orbit around the nucleus.”
Summary – “9. Bohr’s model is applicable only to hydrogenic (single electron) atoms. It cannot be extended to even two electron atoms such as helium.”