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More Last updated date: 30th Nov 2023
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# The spectrum of helium is expected to be similar to that of:(A) $H$ (B) $L{{i}^{+}}$ (C) $Na$ (D) $H{{e}^{+}}$ Verified
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Hint : We know that for this question we must have the knowledge of the Bohr model for hydrogen and hydrogen-like species. We can calculate the radius of the shell by using the atomic number of their respective species in the formula. For fast solving this type of problems just see the valence electrons as core electrons can’t be affected that easily

Let us talk about sodium which has one valence electron but in total it has $11$ electrons and $11$ protons so it will have a complex spectrum and not similar to that of helium.
Now let us talk about $H{{e}^{+}}$ . Now it has one electron and two protons; its spectrum is similar to hydrogen, not helium itself. Now the remaining option which is $L{{i}^{+}}$ so it has three protons but two electrons in its valence shell same as that of helium so its spectrum is similar to that of $L{{i}^{+}}$ .