Which type of electromagnetic radiation can penetrate substances like skin and muscle?

X-rays are a form of electromagnetic radiation that have a high energy level, which enables them to penetrate various materials, including biological tissues like skin and muscle. This penetrative ability is due to their short wavelength and high frequency, allowing them to pass through softer substances while being absorbed by denser materials, such as bones. This characteristic makes X-rays particularly valuable in medical imaging, where they help create images of the internal structures of the body.

In contrast, infrared radiation is primarily associated with heat and is not capable of penetrating skin or muscle significantly. Microwaves, while they can penetrate food and are used in cooking, do not have the energy levels necessary to effectively enter biological tissues for imaging purposes like X-rays. Gamma rays, while also highly penetrating, are more associated with nuclear processes and radiactivity, which place them outside the typical medical imaging context compared to X-rays.