Answer:
λ = 75 µm, correct is A
Explanation:
In waves, speed is related to wavelength and frequency
c = λ f
λ = c / f
in this exercise indicate the frequency of rationality
f = 4 THz = 4 10¹² Hz
let's calculate
λ = 3 10⁸/4 10¹²
λ = 7.5 10⁻⁵ m = 75 10⁻⁶ m
λ = 75 µm
