$X$-rays of which of the following wavelengths are hardest? (in $\mathring{A}$)

In the characteristic $X$-ray spectra of an atom superimposed on a continuous $X$-ray spectrum, identify the peaks $P$ and $Q$ shown in the graph.

If the voltage of an $X$-ray tube is doubled,the intensity of $X$-rays will become

What does the hardness of $X$-rays obtained from an $X$-ray tube indicate?

The minimum wavelength of $X$-rays produced in a Coolidge tube operating at $40 \ kV$ is ..... $\mathring A$.

If the series limit of the Balmer series for hydrogen is $3646 \ \mathring{A}$,calculate the atomic number $(Z)$ of the element which gives an $X$-ray wavelength of the $K_{\alpha}$ line as $1.0 \ \mathring{A}$.