changing frequency of a photon in an elastic collision

[MDwannabe7]

In a Kaplan passage about lightening, we are told that lightening can be induced by large explosions on the Earth's surface that send fireballs up into the atmosphere. The intense rush of high energy photons from the fireball collide with electrons in the air molecules. In these elastic collisions, enough energy is transferred to the electrons so that they can separate from the air molecules - which creates an electric field strong enough to produce lightening. We are later asked "Which of the following is true of the collision between the photon and the electron that leads to fireball induced lightening?"

All of the options include that the collision is either inelastic or elastic and the frequency of the photon either increases or decreases. We know that the collision is elastic, as we are explicitly told that in the passage. However, how is the energy transferred from the photons to the electrons related to the frequency of the photons. We know that c=lambda*f and that lambda can change, but usually frequency does not change. What is the relationship between energy and frequency?

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[HawkeyePostOp]

e = hf

 

[MDwannabe7]

e = hf

Thanks - I feel like I should have been able to figure that out - thanks for getting me out of my brain freeze.