The correct option is (c).
Explanation
Neils Bohr proposed a model of the atom in 1913 to address the limitations of Rutherford’s model, particularly concerning the stability of the atom. By incorporating early quantum theory, Bohr established specific postulates regarding the arrangement and behavior of electrons.
- Statement 1 is Correct: Bohr postulated that electrons revolve around the nucleus only in certain permitted orbits, referred to as "discrete orbits." Unlike classical mechanics, which suggests any orbit is possible, Bohr proposed that only orbits with specific angular momentum are allowed.
- Statement 2 is Incorrect: A crucial feature of Bohr's model is that while revolving in these discrete orbits, electrons do not radiate energy. This postulate contradicts classical electromagnetic theory, which predicts that accelerated charged particles should continuously emit radiation and lose energy. By stating that energy is not lost in these stationary orbits, Bohr explained the stability of the atom.
- Statement 3 is Correct: These discrete orbits are associated with fixed amounts of energy and are known as energy levels or energy shells. They are represented by the letters K, L, M, N, etc., or by the integers n = 1, 2, 3, 4, etc.
Key Takeaway: The Bohr model explains atomic stability by proposing that electrons occupy fixed, discrete energy levels (stationary states) where they revolve without radiating energy.