X-rays, microwaves, and visible light are all forms of electromagnetic radiation, so all listed are electromagnetic waves.

Increasing the tube voltage raises the maximum photon energy, so the minimum (shortest) wavelength decreases.

All bodies emit electromagnetic radiation due to thermal motion; emission is not limited to visibly hot bodies or antennas.

All electromagnetic waves travel at the same speed in vacuum (c) but have different wavelengths.

Range for line-of-sight transmission scales with the square root of antenna height, so covered area ∝ height; doubling area therefore requires doubling the height.

Shorter wavelength X-rays have higher energy and greater penetrating power, so 2 Å penetrates most among the options.

Cathode rays are streams of electrons (particles), not electromagnetic radiation.

With increasing temperature the peak shifts to shorter wavelengths, so shorter-wavelength radiation increases while longer-wavelength radiation decreases.

Among the listed radiations, red light has the longest wavelength; gamma rays and X-rays are far shorter, and blue light is shorter than red.

X-rays have very high frequency compared with visible light and radio waves.