Answer
Cu is probably in the sample.
Work Step by Step
The frequency of the emitted light $\nu=9.23\times10^{14}s^{-1}$
The speed of light in a vacuum $c\approx2.998\times10^8m/s$
We need to calculate the wavelength of the emitted light according to the formula $$\lambda=\frac{c}{\nu}$$$$\lambda=\frac{2.998\times10^8m/s}{9.23\times10^{14}s^{-1}}$$$$\lambda\approx3.248\times10^{-7}m\approx324.8nm$$
$324.8nm$ equals the characteristic wavelength of Cu. Therefore, the sample is most likely to contain Cu.
