The correct answer is A. X-rays.
X-rays have the shortest wavelength of all the types of radiation listed. They are a type of electromagnetic radiation with wavelengths in the range of 0.01 to 10 nanometers. X-rays are used in a variety of medical and industrial applications, such as medical imaging, radiography, and crystallography.
A-rays are a type of alpha radiation. They are helium nuclei that are emitted from radioactive atoms. A-rays have a relatively long wavelength, about 100 times longer than X-rays. A-rays are not very penetrating and can be stopped by a sheet of paper.
B-rays are a type of beta radiation. They are electrons or positrons that are emitted from radioactive atoms. B-rays have a wavelength that is about 100 times shorter than A-rays. B-rays are more penetrating than A-rays, but they can still be stopped by a thin sheet of metal.
G-rays are a type of gamma radiation. They are high-energy photons that are emitted from radioactive atoms. G-rays have the shortest wavelength of all the types of radiation listed. They are very penetrating and can only be stopped by thick layers of lead or concrete.