40-26

$${f = \frac{\Delta E}{h} = \frac{(10,2\, \mathrm{eV})(Z - 1)^2}{(4,14 \times 10^{-15}\, \mathrm{eV \cdot s})} \\ = (2,46 \times 10^{15}\, \mathrm{Hz})(Z - 1)^2}$$