What characterizes soft X-rays compared to hard X-rays?

Soft X-rays are characterized by their lower photon energies and frequencies compared to hard X-rays. This distinction is crucial in understanding their interaction with matter. Soft X-rays typically fall within the energy range of about 0.1 to 10 keV, while hard X-rays have energies greater than 10 keV.

The lower energy of soft X-rays leads to different properties, such as lesser penetration ability through materials. They are more readily absorbed by substances like skin or biological tissues, making them less suitable for applications that require deeper penetration, such as medical imaging or industrial inspections, where hard X-rays are preferred due to their higher energy and greater penetrating power.

While options related to photon energies and frequencies indicate the fundamental difference between soft and hard X-rays, the ability to penetrate materials and the presence of characteristic peaks pertain more specifically to the practical applications of these X-rays rather than defining their basic characteristics as soft or hard. Thus, the correct option highlights the essential physical properties differentiating these two types of X-rays.