When white light hits the water droplets, it gets refracted into seven different colors: violet, indigo, blue, green, yellow, orange and red. They vary in their wavelengths and also in their frequencies.
Wavelength is the distance between two successive crests or two successive troughs. Red has the longest wavelength while violet has the shortest wavelength.
Frequency is the inverse proportional of wavelength. It is the number of crests or troughs that pass a point per second. So, red would have the shortest frequency while violet has the highest frequency.
When white light is passed through a prism it is split into violet, indigo, blue, green, yellow,orange and red colours. The colours are a continuous spectrum of many waves with varying wavelengths and frequencies.
Wavelength: is the distance between successive crests of a wave. The colour red has the longest wavelength and the colour violet the shortest.
Frequency: Can be understood as the number of waves in a given period of time or how compact the wave crests are. Since violet has the shortest wavelength its frequency is the highest and since red has the longest wavelength its frequency is the lowest.