physics question mcq work done

hi, please could I have some help on this question? I'm not sure how the answer is C, work done=fd buit distance sq and sr cannot be the same?
question: https://ibb.co/dJ4gRpVW
thanks!

Since you are doing revision for physics and you have done vector (dot product) in mathematics, it is good to know that work done is the dot product between force and displacement.
Along the displacement SQ, we can write the displacement along i and j independently, while the electric force is just along i.
In computing the work done, the dot product between i (force) and j(displacement) is zero. This is the maths of work done.
What is the physics? It means that the work done by the electric force does not depend on the path taken by the charge.

I'm still unsure, how did you get "the dot product between i (force) and j(displacement) is zero". Is it because they are not in the same direction so work done is 0? But how about the displacement along i, do we not multiply that with the force?