Which of the following is a man-made source of radiation?

Medical x-rays are a prime example of a man-made source of radiation. This technology is utilized extensively in the healthcare field for diagnostic purposes, allowing healthcare professionals to visualize the internal structures of the body without invasive procedures. Medical x-rays are produced by machines specifically designed to generate x-ray photons, which are a form of ionizing radiation.

In contrast, radon gas, cosmic radiation, and terrestrial radiation are all natural sources of background radiation. Radon gas is a radioactive gas that emanates from the decay of uranium in soil and rocks, contributing to natural exposure to radiation in many environments. Cosmic radiation comes from outer space, primarily from the sun and other celestial bodies, and constantly interacts with the Earth's atmosphere. Terrestrial radiation is emitted from radioactive materials present in the Earth's crust, such as uranium, thorium, and potassium-40. These sources of radiation are not man-made but rather occur naturally in our environment.

Therefore, the distinction of medical x-rays as a man-made source highlights their significance in the medical field while the other options emphasize natural sources of radiation exposure that all individuals experience to varying degrees.