iron and nickel carbon and oxygen nitrogen and sulfur hydrogen and helium
I gave my students this multiple choice question: The frost line of the solar system divides the terrestrial plants from the gas-giant planets. What elements make up most of the core of the planets orbiting outside of the frost line?

Only one answer is correct among these 4 choices:
- iron and nickel
- carbon and oxygen
- nitrogen and sulfur
- hydrogen and helium

Could you tell me which one is correct?

hydrogen and helium