Which type of radiation has very short (<10 –3 nm) wavelengths, produced by nuclear explosions, lightning and less dramatic activity of radioactive decay?

Correct — D. The stem fixes the wavelength at less than 10⁻³ nm — a picometre, shorter than anything else on the electromagnetic spectrum.

Only gamma rays sit that far down. They are emitted when an unstable nucleus sheds energy, which is exactly why the stem names nuclear explosions and radioactive decay as their sources → option (d).

Why the others are wrong

• (a)
  Microwave — Microwaves are the long end of the four, roughly 1 mm to 1 m. They come from ovens, radar and mobile networks — a billion times longer than the wavelength the stem specifies.
• (b)
  Infra-red — Infrared runs from about 700 nm to 1 mm, longer than visible light. Every warm body emits it and we feel it as heat; nothing about it requires a nucleus.
• (c)
  Ultraviolet — Ultraviolet is roughly 10-400 nm. That is short, but still many thousand times longer than 10⁻³ nm, and its usual source is the Sun rather than radioactive decay.

The electromagnetic spectrum runs, from shortest wavelength to longest: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves.

Wavelength and frequency move in opposite directions, and photon energy follows frequency. So the shortest waves carry the most energy per photon, which is why gamma rays penetrate deepest and need lead or thick concrete to stop them.

Source is the surest way to tell gamma from X-rays: gamma comes out of the nucleus, X-rays come from electrons.

Key facts

• From shortest wavelength to longest: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves.
• Gamma rays originate in the nucleus during radioactive decay, while X-rays originate from electrons.
• One nanometre is 10⁻⁹ m, so the stem's 10⁻³ nm is one picometre.
• Shorter wavelength means higher frequency and higher photon energy, which is why gamma radiation is the most penetrating.

Common traps

• Ordering the spectrum by frequency and then answering as if the question had asked for wavelength.
• Choosing ultraviolet because it is the radiation students hear most about, although its wavelength is far too long for the stem.

No directly related past PYQ was found.