Which of the following properties of x-rays allows them to cause ionization?

The property that allows x-rays to cause ionization is their ability to affect photographic film. X-rays are a form of electromagnetic radiation that possess sufficient energy to knock electrons from atoms, which results in the formation of ions. This ionization capability is a critical aspect of x-ray technology and underpins its application in imaging and medical diagnostics.

When x-rays interact with matter, such as the silver halide crystals in photographic film, they can cause a chemical change, leading to the blackening of the film. This effect is due to the energy of the x-rays being sufficient to displace electrons, creating ions and free radicals that can further react with compounds in the film. This interaction illustrates the ionizing nature of x-rays, thereby enabling their use in creating images.

Other options, while they describe certain characteristics of x-rays, do not directly relate to their ability to cause ionization. For example, x-rays do not have weight in the conventional sense, as they are massless photons. Traveling at the speed of sound is inaccurate, as x-rays travel at the speed of light, which is significantly faster. Lastly, the invisibility of x-rays does not contribute to their ionizing effects; instead, it pertains to their detection and imaging capabilities.