Final answer:
The scattering angle at which incident 100 keV particles will be scattered through 180 degrees depends on the particles involved and requires additional context for a precise answer.
Step-by-step explanation:
The scattering angle for which incident 100 keV particles will be scattered through 180 degrees can only be determined by knowing the type of particles involved (like electrons, protons, etc.) and considering the conservation of momentum and energy in elastic collisions. Factors such as the scattering medium and the masses of the involved particles will affect the answer. Compton scattering, for instance, describes the scattering of photons off electrons and there is a specific Compton formula that relates the change in the photon's wavelength to the angle of scattering, but it does not apply to 'particles' such as electrons or protons in a straightforward manner without additional context.