Which molecules produced during the Krebs cycle are used in the electron transport chain?
NADH and FADH (although FADH is very short lived, as it is immobile and covalently bound to complex II of the electron transport chain already, so one could argue that the molecule from the cycle that it actually uses is succinate, or even that the Krebs cycle produces ubuiqinol rather than FADH, and it is this that is used in the electron transport chain).