Ionisation in a gas cannot be produced by

In obtaining an $\mathrm{X}$-Ray photograph of our hand we use the principle of

A metal block is exposed to beams of $\mathrm{X}$-Rays of different wavelengths. Which of the $\mathrm{X}$-Rays, having following wavelengths, penetrate most

The $\mathrm{X}$-Ray beam coming from an $X$-ray tube will be