Easy MCQ +4 / -1 PYQ · JEE Mains 2025

Assuming the validity of Bohr's atomic model for hydrogen like ions the radius of $\mathrm{Li}^{++}$ ion in its ground state is given by $\frac{1}{X} a_0$, where $X=$ __________ (Where $\mathrm{a}_0$ is the first Bohr's radius.)

  1. A 2
  2. B 9
  3. C 1
  4. D 3 Correct answer

Solution

<p>The radius of a hydrogen-like ion according to Bohr's atomic model is given by the formula:</p> <p>$ r = r_0 \frac{n^2}{Z} $</p> <p>Where:</p> <p><p>$ r_0 $ is the first Bohr radius ($ a_0 $)</p></p> <p><p>$ n $ represents the principal quantum number</p></p> <p><p>$ Z $ is the atomic number of the ion</p></p> <p>For the ion $ \text{Li}^{++} $, the atomic number $ Z = 3 $ and we are considering the ground state, so $ n = 1 $.</p> <p>Plugging these values into the formula, we get:</p> <p>$ r = r_0 \frac{1^2}{3} = \frac{r_0}{3} $</p> <p>This shows that the radius of $\text{Li}^{++}$ in its ground state is $\frac{1}{3} a_0$, meaning $ X = 3 $.</p>

About this question

Subject: Physics · Chapter: Atoms and Nuclei · Topic: Bohr's Model of Hydrogen Atom

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