A metal surface ejects electrons when hit by green light but does not eject electrons when hit by yellow light. The electrons will be ejected when the surface is hit by ______.

The order of frequencies of different colors of visible light are as follows:

Violet > Indigo > Blue > Green > Yellow > Orange > Red

The photoelectric emission is possible when frequency of incident light is greater than the threshold frequency. 

Here, frequency of green light is more than threshold frequency of metal but frequency of yellow light is less than threshold frequency.

So, the photoelectric emission is possible for all the lights which have frequency more than or equal to that of green light.

Infra-red and heat waves have lower frequencies than the visible light.

Out of the given options, blue light is having higher frequency than that of green light.