Problem

If the frequency of

K_\alpha

X-ray emitted from the element with atomic number 31 is

f

, then the frequency of

K_\alpha

X-ray emitted from the element with atomic number 51 would be a.

\frac{5f}{3}

\frac{51f}{31}

\frac{9f}{25}

\frac{25f}{9}