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

The energy of a photon of light with wavelength $5000\,\mathring{A}$ is approximately $2.5\,\text{eV}$. In this way,the energy of an $X$-ray photon with wavelength $1\,\mathring{A}$ would be:

When the atomic number of the first target is $Z_1 = 64$ and the atomic number of the second target is $Z_2 = 80$,the approximate ratio of the wavelengths of the $K_{\alpha,1}$ and $K_{\alpha,2}$ radiations is .......

Characteristic $X$-rays:

$X$-rays are produced due to which of the following?

The energy of an $X$-ray photon of wavelength $1.65 \mathring{A}$ is ....... $keV$. $(h = 6.6 \times 10^{-34} \ J \cdot s, \ c = 3 \times 10^8 \ m/s, \ 1 \ eV = 1.6 \times 10^{-19} \ J)$ (in $.5$)