According to the Bohr's model of the atom, electrons in an atom absorb energy to move from a lower to higher energy level.
We must note that as we progress away from the nucleus, the energy levels of electrons become closer together. The energy difference between successive levels decreases and the wavelength of light associated with such transitions become longer.
Hence,the absorption of light of the longest wavelength corresponds to n = 3 to n = 5
By sharing electeons with each other if they lose or gain electrons then they only form ions they cannot lose neutrons as they are locked inside the nucleus
