Which of the following describes characteristic X-rays?

Characteristic X-rays are indeed described as high-intensity peaks at specific frequencies. This is due to the nature of how they are produced. When inner-shell electrons in a target material are ejected—typically through the interaction with high-energy incoming electrons—an electron from a higher energy level will fall into that vacancy.

This transition of electrons from one energy level to another results in the release of energy in the form of X-rays, which are emitted at specific energies that correspond to the differences in energy levels of the electrons in the atoms of the target material. These specific energies translate to particular frequencies of emitted X-rays, leading to the appearance of discrete spectral peaks when plotted on a graph of intensity versus frequency.

This phenomenon contrasts with broad-spectrum emission, which consists of a wide range of frequencies without distinct peaks. Thus, the identification of characteristic X-rays by their high-intensity peaks at specific frequencies is fundamental in both practical applications and analytical techniques within physics and materials science.