Which of the following wavelengths falls in the $X-$ray region in $\mathring{A}$?

The wavelength of the $L_\alpha$ $X$-ray line of $Pt^{78}$ is $1.32 \, \mathring A$. The wavelength of the $L_\alpha$ line in the $X$-ray spectrum of another unknown element is $4.17 \, \mathring A$. If the screening constant for the $L_\alpha$ line is $7.4$,then the atomic number of the unknown element is:

The voltage applied across an $X$-ray tube is nearly......$V$.

The binding energy of the innermost electron in tungsten is $40 \, keV$. The energy of the characteristic $X$-rays emitted is:

The ${K_{\alpha}}$ $X$-rays arising from a cobalt $(Z = 27)$ target have a wavelength of $179\, pm$. The ${K_{\alpha}}$ $X$-rays arising from a nickel target $(Z = 28)$ is

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