Answer:
Step-by-step explanation:
wavelength of light = 4 x 10⁻⁷ m
frequency = velocity in air / 4 x 10⁻⁷
= 3 x 10⁸ / 4 x 10⁻⁷
= .75 x 10¹⁵ Hz
= 75 x 10¹³ Hz.
Wave length = 4 x 10⁻⁷ m
= 400 x 10⁻⁹m
400 nm
colour of light having this wavelength in air is violet .