Who invented $X-$rays?

When cathode rays strike a metal target with a high melting point and high atomic number,what is produced?

If $\lambda_{Cu}$ is the wavelength of the $K_{\alpha}$ $X$-ray line of copper (atomic number $Z = 29$) and $\lambda_{Mo}$ is the wavelength of the $K_{\alpha}$ $X$-ray line of molybdenum (atomic number $Z = 42$),then the ratio $\frac{\lambda_{Cu}}{\lambda_{Mo}}$ is close to:

The continuous $X-$ray spectrum produced by an $X-$ray machine at constant voltage has

For harder $X$-rays:

$A$ metal block is exposed to beams of $X$-rays of different wavelengths. $X$-rays of which wavelength penetrate most?