Electromagnetic spectrum frequency ranges

Steps:

• Recall standard frequency ranges: radio waves (< 3×10^9 Hz), infrared (3×10^11 to 4×10^14 Hz), ultraviolet (7.5×10^14 to 3×10^16 Hz), X-rays (> 3×10^16 Hz).
• Convert 10^14 Hz to 100 THz for reference.
• Compare 10^14 Hz to infrared range (0.3–400 THz).
• Confirm it matches infrared, not adjacent regions.

Why A is correct:

• Infrared waves span frequencies from 3×10^11 Hz to 4×10^14 Hz, directly including 10^14 Hz per standard EM spectrum classification.

Why the others are wrong:

• B. Ultraviolet waves begin at about 7.5×10^14 Hz, exceeding 10^14 Hz.
• C. Radio waves have frequencies below 3×10^9 Hz, far lower than 10^14 Hz.
• D. X-rays start above 3×10^16 Hz, much higher than 10^14 Hz.

Final answer: A