Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: outermost layer of the sun, made up of a plasma that extends millions of kilometers into space. Answer: plasma
[A]: What is the outer layer of the sun made up of?

[Q]: Passage: Resistance is the property that determines the amount of current flow through a particular material. Answer: resistance
[A]: What is the property that determines the amount of current flow through a particular material?

[Q]: Passage: The energy of a photon is directly proportional to the frequency of the electromagnetic radiation. Answer: radiation
[A]:
The energy of a photon is directly proportional to the frequency of the electromagnetic what?