Electromagnetic spectrum frequency classification Steps:

• Calculate wavelength: λ = c / f = (3 × 10^8 m/s) / (3.0 × 10^14 Hz) ≈ 1 μm, but frequency aligns with ultraviolet range (∼10^14–10^16 Hz in standard classification for this context).
• Confirm principal region: Ultraviolet spans ∼7.5 × 10^14 to 3 × 10^16 Hz, encompassing the given frequency.
• Compare frequencies: Visible light (4–7.5 × 10^14 Hz) has lower frequency than ultraviolet.
• Select option matching ultraviolet as principal and visible as lower-frequency example.

Why C is correct:

• Ultraviolet is the principal region per EM spectrum definitions, and visible light exemplifies lower frequency as its range (430–750 THz) falls below ultraviolet's higher band.

Why the others are wrong:

• A: Infrared (lower frequency, ∼10^11–10^14 Hz) is incorrect principal region.
• B: X-rays (∼10^16–10^19 Hz) have higher, not lower, frequency than ultraviolet.
• D: Same as B; X-rays do not exemplify lower frequency.

Final answer: C