According to Bohr’s first postulate, an electron in an atom can revolve
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → In certain stable orbits without emission of radiant energy
Bohr’s first postulate: an electron in an atom can revolve only in certain stable orbits (stationary states) and, while in them, does not radiate energy, contrary to classical electromagnetic theory.
The second postulate fixes which orbits are allowed (angular momentum \( mvr = nh/2\pi \)); the third says that radiation is emitted only when the electron jumps between orbits.
NCERT (2026-27):
Bohr Model of the Hydrogen Atom – “… (i) Bohr’s first postulate was that an electron in an atom could revolve in certain stable orbits without the emission of radiant energy, contrary to the predictions of electromagnetic theory.”