The relationship between energy ($E$) and wavelength ($\lambda$) is given by $\lambda = \frac{hc}{E}$. Using the value $hc \approx 1240 \text{ eV nm}$ and converting the given energy to eV ($15 \text{ keV} = 15,000 \text{ eV}$): $\lambda = \frac{1240 \text{ eV nm}}{15000 \text{ eV}} \approx 0.083 \text{ nm}$ According to the electromagnetic spectrum, X-rays have a wavelength range typically from $1 \text{ nm}$ to $10^{-3} \text{ nm}$ . Since $0.083 \text{ nm}$ falls within this range, the electromagnetic wave belongs to the X-ray region. Gamma rays typically have wavelengths less than $10^{-3} \text{ nm}$ (energies $> 100 \text{ keV}$), while UV rays are in the range $400 \text{ nm}$ to $1 \text{ nm}$.