What is activation energy for the forward reaction represented in the energy diagram?

+200 kj

+350 kj

+150 kj

+250 kj
done

So your activation energy is the distance between the potential energy of your reactants (which is the flat line in the left of the diagram) and the peak (which is the highest point in the diagram). From the looks of it, the peak of the diagram is at 450 kJ. Your reactants are at 200 kJ. 

Subtract 450 from 200, and you're at your answer!

What are the choices?

C) electrons encircling a nucleus with neutrons and protons