Q.Why are microwaves used in radar?

In order of increasing frequency, the electromagnetic spectrum runs radio waves -> microwaves -> infrared -> visible -> ultraviolet -> X-rays -> gamma rays, so microwaves have a higher frequency than radio waves but lower frequency than infrared, visible or UV.

Radio waves: roughly a few Hz up to about 10^9 Hz (~1 GHz).

Microwaves: roughly 10^9 Hz to 3 x 10^11 Hz (1 GHz to 300 GHz), i.e. above the radio band.

Infrared, visible light and UV all have still-higher frequencies than microwaves.

So among the options, only "more than the frequency of radio waves" is correct; microwave frequency is NOT more than infrared or visible light.

Microwaves suit radar because their short wavelength gives sharp, directional beams and good penetration through weather.

Radar needs to accurately locate the direction, distance and speed of an aircraft. Because microwaves have a short wavelength (mm–cm range) compared to ordinary radio waves, they can be formed into a narrow, highly directional beam using a comparatively small antenna/dish (diffraction spreading is small when wavelength << aperture size). This narrow beam lets radar pinpoint direction precisely, and the reflected pulse gives distance (from time delay) and speed (from Doppler shift). Microwaves also readily penetrate clouds, fog and haze, so they still function in poor visibility — exactly what aircraft navigation radar needs.

Radar systems use microwaves because they combine good penetration through the atmosphere with the ability to be focused into narrow beams for precise target detection. The correct option is (C).

Microwave ovens use microwaves (typically ~2.45 GHz) to heat food by agitating water molecules; microwaves and radio waves are different, though neighbouring, bands of the EM spectrum.

In the electromagnetic spectrum, radio waves and microwaves are separately classified bands — radio waves have longer wavelengths/lower frequencies (used for broadcasting/communication), while microwaves have shorter wavelengths and higher frequencies (roughly 1 mm to 1 m, or 300 MHz–300 GHz). A microwave oven generates microwaves (about 2.45 GHz) using a magnetron; these waves are absorbed by water, fat and sugar molecules in food, causing them to vibrate rapidly and generate heat. This operating principle is specifically based on microwaves, not the lower-frequency radio waves used for broadcasting.

A magnetron is a vacuum-tube device that generates microwaves, used e.g. in radar and microwave ovens.

A magnetron uses a strong magnetic field together with an accelerating electric field inside a vacuum tube to make electrons execute curved paths past a set of resonant cavities, causing them to give up energy as electromagnetic radiation in the microwave frequency range (roughly GHz). This is the standard source used to generate microwaves in radar systems and microwave ovens.

Microwaves occupy the electromagnetic spectrum roughly from 1 GHz to 300 GHz.

Microwaves are electromagnetic waves lying between radio waves and infrared radiation, with wavelengths from about 1 mm to 1 m. This corresponds to frequencies of order $10^{9}$ Hz to $10^{11}$ Hz, i.e., in the gigahertz (GHz) range. They are produced by special vacuum tubes (klystrons, magnetrons, Gunn diodes) and are used in radar and microwave ovens.

Microwaves (short-wavelength radio waves) are ideal for point-to-point communication because of their high frequency and ability to be focused into narrow beams with small antennas.

The electromagnetic spectrum includes radio waves, microwaves, infrared, visible, ultraviolet, X-rays and gamma rays, each suited to different applications based on wavelength/frequency.

Microwaves (roughly mm to a few cm wavelength) can be transmitted as narrow beams using small dish antennas, and are used for telecommunications — mobile phones, satellite communication, radar, and point-to-point microwave links — because of their high information-carrying capacity and directional transmission.

Ultraviolet, visible and infrared are used mainly for other purposes (sterilisation, illumination/vision, thermal imaging/remote controls respectively), not as primary telecommunication carriers.

Radar needs a highly directional beam and precise object-location capability; microwaves' short wavelength (compared to radio waves) makes both possible.

Radar (RAdio Detection And Ranging) works by transmitting electromagnetic pulses toward a target and analysing the reflected (echoed) signal to determine the target's distance, direction and speed. For this to work well:

1. Directionality: By diffraction theory, the spreading of a wave is significant when its wavelength is comparable to the size of the aperture (antenna). Since microwaves have very small wavelengths (millimetres to centimetres), a relatively small antenna/dish can produce a narrow, well-collimated beam — essential for precisely locating a target's direction.

2. Good reflection from small objects: Objects such as aircraft, ships, or storm clouds reflect electromagnetic waves efficiently when the wavelength is comparable to or smaller than the object size. Microwaves, being short-wavelength, reflect strongly off such objects, producing a detectable echo.

3. High information-carrying capacity: Their high frequency also allows a larger bandwidth for carrying the pulsed signal information.

For these reasons — narrow directional beams and strong, precise reflection — microwaves are the preferred electromagnetic waves for radar systems.