Hi Victoria,

I'm pretty sure your CC puts it in terms of ATP, where NADH yields 3 ATP and FADH2 yields 2 ATP - this is likely where the confusion comes from.

In more complicated cases they might ask you about number of protons instead, where NADH pumps 10 H+ into the intermembrane space, and FADH2 pumps in 6 H+.

For this, I've drawn a more detailed picture of how proton transport through the ETC works:

https://ibb.co/25TppRy

It takes 3 H+ to make 1 ATP by ATP sythase on average, so you can always take the amount of ATP made per molecule if you know that and multiply it by three.

This is a question that can come up on the topic of oxidative phosphorylation. It is a little more advanced than the coverage in the CC.

Hope this helps!

Katt