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Atoms and Nuclei question

2003 · Shift 0 · Q120
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Atoms and Nuclei question

2003 · Shift 0 · Q120

JEE MainPhysicsAtoms and NucleiMCQ+4 / −1
If the binding energy of the electron in a hydrogen atom is 13.6eV,13.6eV,13.6eV, the energy required to remove the electron from the first excited state of Li++L{i^{ + + }}Li++ is
  1. A
    30.6eV30.6eV30.6eV
  2. B
    13.6eV13.6eV13.6eV
  3. C
    3.4eV3.4eV3.4eV
  4. D
    122.4eV122.4eV122.4eV
View written solutionFree

Correct answer: A

  1. Identify the species

    The ion is Li++\mathrm{Li^{++}}Li++, which is a hydrogen-like ion with: Z=3Z=3Z=3 because lithium has atomic number 333 and Li++\mathrm{Li^{++}}Li++ has only one electron left.

  2. Use the energy formula for a hydrogen-like atom

    For a hydrogen-like species, the energy of the electron in the nnnth orbit is: En=−13.6Z2n2 eVE_n=-13.6\frac{Z^2}{n^2}\,\text{eV}En​=−13.6n2Z2​eV

    Here, for Li++\mathrm{Li^{++}}Li++: En=−13.632n2=−13.69n2 eVE_n=-13.6\frac{3^2}{n^2}=-13.6\frac{9}{n^2}\,\text{eV}En​=−13.6n232​=−13.6n29​eV

  3. First excited state

    The first excited state corresponds to: n=2n=2n=2

    So, E2=−13.694=−30.6 eVE_2=-13.6\frac{9}{4}=-30.6\,\text{eV}E2​=−13.649​=−30.6eV

  4. Energy required to remove the electron

    To remove the electron from this state, we must take it from E2=−30.6 eVE_2=-30.6\,\text{eV}E2​=−30.6eV to 0 eV0\,\text{eV}0eV.

    Therefore, required energy is: ΔE=0−(−30.6)=30.6 eV\Delta E=0-(-30.6)=30.6\,\text{eV}ΔE=0−(−30.6)=30.6eV

  5. Check options

    • A: 30.6 eV30.6\,\text{eV}30.6eV ✅
    • B: 13.6 eV13.6\,\text{eV}13.6eV ❌
    • C: 3.4 eV3.4\,\text{eV}3.4eV ❌
    • D: 122.4 eV122.4\,\text{eV}122.4eV ❌

Thus, the correct answer is Option A.

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