Light color determines frequency

Steps:

• Red and green are different colors of visible light.
• Color corresponds to electromagnetic wave frequency, with red at lower frequencies (~4.3×10^14 Hz) and green higher (~5.5×10^14 Hz).
• In vacuum, light speed is constant (c = 3×10^8 m/s), so frequency differs if wavelengths differ.
• Lasers can emit same or different amplitudes/intensities, but color requires frequency difference.

Why B is correct:

• Frequency defines visible light color per the electromagnetic spectrum; red light has lower frequency than green (ν = c/λ, where λ_red > λ_green).

Why the others are wrong:

• A: Amplitude relates to electric field strength and can be identical for both beams.
• C: Intensity (power per area) depends on photon flux and can be equal regardless of color.
• D: All electromagnetic waves travel at speed c in vacuum, independent of frequency.

Final answer: B