What characteristic of x-rays increases with higher energy?

The characteristic of x-rays that increases with higher energy is their penetrability. As the energy of x-rays increases, their ability to penetrate through materials (such as human tissue or other substances) also improves. Higher energy x-rays have shorter wavelengths, allowing them to traverse denser materials without being absorbed or scattered as readily as lower energy x-rays.

This property is crucial in medical imaging and radiation therapy, where the goal is often to ensure that x-rays can effectively pass through certain areas while minimizing exposure to surrounding healthy tissues. The effectiveness of x-rays in diagnostic and therapeutic contexts relies heavily on their penetrative ability, which is intrinsically linked to their energy levels.

In contrast, other options are not applicable: the wavelength decreases with higher energy, x-rays do not have mass in the traditional sense being photons, and while higher energy x-rays may have different absorption characteristics, absorption typically increases with lower energy due to the interactions with matter.