Which of the arrangements of radiations below shows decreasing order of wavelengths?

Analyze the question: You are asked to arrange the radiations from the longest wavelength to the shortest (decreasing order of wavelength).

Concept: All of these are electromagnetic waves. They travel at the same speed in a vacuum, c = fλ, so wavelength is inversely proportional to frequency. A higher frequency means a shorter wavelength.

The electromagnetic spectrum, from longest to shortest wavelength:

Radio waves > Microwaves > Infrared > Visible light > Ultraviolet > X-rays > Gamma rays

Solution:

• Radio waves have wavelengths from about 1 mm to several kilometres.
• Infrared has wavelengths of about 700 nm to 1 mm.
• X-rays have wavelengths of about 0.01 nm to 10 nm.

So the decreasing order of wavelength is:

Radio waves > Infrared radiations > X-rays

Checking the options:

• A: X-rays are placed first, which is wrong.
• B: Radio waves > infrared > X-rays, which is correct.
• C: Infrared is placed above radio waves, which is wrong.
• D: X-rays are placed first, which is wrong.

Tip: Remember the spectrum with the phrase "Raging Martians Invaded Venus Using X-ray Guns" (Radio, Microwave, Infrared, Visible, Ultraviolet, X-rays, Gamma). Going left to right, wavelength decreases while frequency and energy increase. If a question asks for increasing order, just reverse the list.