An element of atomic number 9 emits `K_(alpha)` X-ray of wavelength `lamda`. Find the atomic number of the element which emits `K_(alpha)` X-ray of wavelength `4lamda`.

Explanation

For `K_(alpha)` X-ray, `(Z-1)^2lamda=`constant. Hence,
`(9-1)^2lamda=(Z-1)^2(4lamda)`
`(Z-1)^2=(64)/(4)=16`
`Z-1=4` or `Z=5`