Given below are two statements: one is labelled as A s s e r t i o n A and the other is labelled as Reason R
Assertion A : The Bohr model is applicable to hydrogen and hydrogen-like atoms only.
Reason R : The formulation of Bohr model does not include repulsive force between electrons.
In the light of the above statements, choose the correct answer from the options given below

Solution

Physics sir · 4 steps

Bohr's force balance has no electron-electron repulsion, so his model stops at one electron.

1. Check A. Bohr's formulas rₙ ∝ n²/Z and Eₙ = -13.6 Z²/n² eV work for H, He⁺, Li²⁺ and other one-electron species. They fail for neutral helium and for every atom with two or more electrons, so A is true.
2. Check R. Bohr balances only the nucleus-electron attraction against the centripetal requirement. No term for the push of one electron on another appears anywhere, so R is true.

   mv²/r = kZe²/r²

3. Link them. With two or more electrons, each electron also feels the repulsion of the others, so this single force balance no longer describes its motion. A one-electron atom has no such repulsion, and that is why the model works only there. R explains A.
4. So. Both statements are true and R is the correct explanation of A, which is option (b).

The idea to keep. Bohr's model uses one force, the nucleus pulling the electron. A second electron adds repulsion the model cannot handle, so it works only for one-electron species.

Answer from the NTA final answer key. Solution by PrepWiser.