When are characteristic $X$-ray emissions produced?

The shortest wavelength of $X-$rays emitted from an $X-$ray tube depends upon

The potential difference between the cathode and the target in a Coolidge tube is $100 \ kV$. The minimum wavelength of the $X$-rays emitted by the tube is

Stopping potentials of $24, 100, 110$ and $115 \ kV$ are measured for photoelectrons emitted from a certain element (with $24 \ kV$ minimum) when it is irradiated with monochromatic $X-rays$. If this element is used as a target in an $X-ray$ tube,what will be the wavelength of the $K_{\alpha}$ line?

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

In an $X$-ray tube, electrons emitted from a filament (cathode) carrying current $I$ hit a target (anode) at a distance $d$ from the cathode. The target is kept at a potential $V$ higher than the cathode, resulting in the emission of continuous and characteristic $X$-rays. If the filament current $I$ is decreased to $I/2$, the potential difference $V$ is increased to $2V$, and the separation distance $d$ is reduced to $d/2$, then:
$(A)$ The cut-off wavelength will reduce to half, and the wavelengths of the characteristic $X$-rays will remain the same.
$(B)$ The cut-off wavelength as well as the wavelengths of the characteristic $X$-rays will remain the same.
$(C)$ The cut-off wavelength will reduce to half, and the intensities of all the $X$-rays will decrease.
$(D)$ The cut-off wavelength will become two times larger, and the intensity of all the $X$-rays will decrease.