JEE Main · 2021 · Shift-IImediumATOM-130

Statement I: Bohr's theory accounts for stability and line spectrum of Li+ ion. Statement II: Bohr's theory was unable…

Structure of Atom · Class 11 · JEE Main Previous Year Question

Question

Statement I: Bohr's theory accounts for stability and line spectrum of Li+\mathrm{Li^+} ion. Statement II: Bohr's theory was unable to explain the splitting of spectral lines in the presence of a magnetic field.

Choose the most appropriate answer from the options given below:

Options
  1. a

    Both Statement I and Statement II are true.

  2. b

    Statement I is false but Statement II is true.

  3. c

    Both Statement I and Statement II are false.

  4. d

    Statement I is true but Statement II is false.

Correct Answera

Both Statement I and Statement II are true.

Detailed Solution

🧠 The "One-Electron" Filter Bohr's model is famously exclusive. It works flawlessly for any species with exactly one electron (Hydrogenic), but fails the moment a second electron introduces repulsion.

🗺️ The Statement Analysis

  • Statement I: Li2+\mathrm{Li^{2+}} (and likely intended here despite the Li+\mathrm{Li^+} typo in some versions) is a 1-electron system (Z=3,e=32=1Z=3, e=3-2=1). Bohr's theory correctly maps its energy levels and line spectrum. (TRUE)
  • Statement II: Bohr's model treats the atom as a flat, 2D solar system. It has no explanation for why spectral lines split into multiples when placed in a magnetic field (the Zeeman Effect). (TRUE)

The Zeeman/Stark Wall Bohr's inability to explain "splitting" (magnetic = Zeeman, electric = Stark) was the major signal that the model needed to be replaced by full quantum mechanics.

⚠️ Common Traps Be careful with the electron count. Li+\mathrm{Li^+} has 2 electrons and Bohr does not work for it. However, in the context of this JEE question, it is generally treated as an application to hydrogen-like species (Li2+\mathrm{Li^{2+}}).

Answer: (a)\boxed{\text{Answer: (a)}}

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