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The ground state energy of H-atom 13.6 eV. The energy needed to ionize H-atom from its second excited state.

1. 1.51 eV
2. 3.4 eV
3. 13.6 eV
4. 12.1 eV

Correct answer: 3.4 eV

Solution

The second excited state corresponds to n=3. The energy of the nth state is given by E_n = -13.6/n² eV. For n=3, E_3 = -13.6/9 = -1.51 eV. To ionize, the energy required is the difference between 0 eV (ionized state) and -1.51 eV, which is 1.51 eV.

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