What is the wavelength of light emitted when the electron of a hydrogen atom undergoes a transition from an energy level with `n= 4` to an energy level with `n = 2` ? What is the colour corresponding to this wavelength?

Explanation

`bar(v)=R(1/n_(1)^(2)-1/n_(2)^(2))=109677 (1/2^(2)-1/4^(2)) cm^(-1) =20564.4 cm^(-1)`
`lambda =1/v=1/(20564.4 cm^(-1))=486xx10^(-7) cm=486xx10^(-9) m=486 nm`
The colour corresponding to this wavelength is blue.