if the frequency of `K_a` X-ray emitted from the element with atomic number 31 is f, then the frequency of `K_a` x-ray emitted from the element with atomic number 51 would be

Options

A. `(5f)/(3)`
B. `(41f)/(31)`
C. `(9f)/(25)`
D. ` (25f)/(9)`

Answer

D

Explanation

`f prop (Z-1)^(2)` for K-series
`" " (f')/(f)=((51-1)^(2))/((31-1)^(2))=(25)/(9)`
`:. " " f'=(25)/(9)f`