Infrared Radiation as Electromagnetic Wave

Steps:

• Identify infrared as part of the electromagnetic spectrum, like visible light and radio waves.
• Recall electromagnetic waves propagate at speed $c = 3 \times 10^8$ m/s in vacuum, regardless of frequency.
• Compare options: A matches wave speed; B confuses with sound waves; C reverses frequency order; D misapplies emission laws.

Why A is correct:

• All electromagnetic radiation, including infrared, travels at the speed of light in vacuum per Maxwell's equations.

Why the others are wrong:

• B: Infrared is transverse, not longitudinal like sound.
• C: Infrared has lower frequency than ultraviolet.
• D: Black surfaces emit infrared better than white per Kirchhoff's law of thermal radiation.

Final answer: A