JEE MAIN - Physics (2003 - No. 6)

If the binding energy of the electron in a hydrogen atom is $$13.6eV,$$ the energy required to remove the electron from the first excited state of $$L{i^{ + + }}$$ is
$$30.6$$ $$eV$$
$$13.6$$ $$eV$$
$$3.4$$ $$eV$$
$$122.4$$ $$eV$$

Explanation

$${E_n} = - {{13.6} \over {{n^2}}}{Z^2}eV/$$atom

For lithium ion $$Z=3;$$ $$n=2$$ (for first excited state)

$${E_n} = - {{13.6} \over {{2^2}}} \times {3^2} = - 30.6eV$$

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