What is the change in energy ΔE of the hydrogen atom as the electron makes the transition from the n=3 energy?

A) What is the change in energy ΔE of the hydrogen atom as the electron makes the transition from the n=3 energy level to the n=1 energy level?

B) When an atom makes a transition from a higher energy level to a lower one, a photon is released. What is the wavelength of the photon that is emitted from the atom during the transition from n=3 to n=1?

C) When the hydrogen atom makes the transition from the n=2 to the n=1 energy level, it emits a photon. This photon can be absorbed by to a singly ionized helium atom (He ) in its second energy level (ninitial=2), causing it to move to a higher energy level. To what final energy level number nfinal can the photon promote the helium ion?
Note that He has two protons in its nucleus and a single electron.

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