Question

the ratio of velocity of visible light of wavelength 4000 armstrong and infrared ray of wavelength 9000 armstrong in free space is

Answer 1

according to the electromagnetic theory all electromagnetic waves travel in free space with a speed equals to speed of light in vacuum (2.997×(10^8) m/s).
since visible light and infrared waves are both electromagnetic waves so they have same speed in vacuum or free space .
so the ratio is 1:1

Answer 2

the ratio of velocities 2.25