Question

The spectrum of helium is expected to be similar to that of:
(A) $ H $
(B) $ L{{i}^{+}} $
(C) $ Na $
(D) $ H{{e}^{+}} $

Answer 1

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

Complete Step By Step Answer:
Let us know the reason for the emission of spectrum in atom. So when an atom is radiated with radiation having energy the valence electron of that atom gets excited by absorbing the radiation and goes to an excited state by jumping to higher shells. Now it is unstable there so it will come back to its original state that is its ground state by emitting the energy which it has absorbed. So the jumps it takes from excited state to ground state cause the emission of spectrum and hence we get our spectrum. The reason for the spectrum is electrons present in the valence shell so check the valence number of electrons for easiness.
By looking at our first option which is hydrogen it is also the simplest type of atom known because it has a single proton and a single electron which revolve around it .And that of helium it has two protons and two electrons with its s shell completely filled so these two atoms will not have similar spectrum.
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}^{+}} $ .
Therefore the correct answer is option B.

Note :
Remember that the emission spectrum of hydrogen has been divided into different series based on the lower energy level to which the electron transitions are taking place. The Balmer series is the name given for the spectral emissions of hydrogen which arise due to the transition from higher energy levels to the energy level with principal quantum number.