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Ionisation energy of an electron in third excited state for hydrogen atom is _____ eV.

Asked in GSEB Board July 2021 · Energy levels and ionisation

Answer: (3) 0.85

Step-by-step solution

Idea: counting the ground state as n=1, the first, second and third excited states are n=2, 3 and 4.

So the electron is in n=4.

E₄=-(13.6)/(4²)=-(13.6)/(16)=-0.85 eV.

Ionisation takes the electron to n=∞, where its energy is zero.

Energy needed =0-E₄=0.85 eV.

Why the other options are wrong

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