Question

How many protons are accumulated in intermembrane space of mitochondria from one molecule of $NADH$ during $ETS$?

Answer 1

Electrons accumulated in the intermembrane space

In complex I, the oxidation of $NADH$ releases electrons which is transported to ubiquinone which is present in the inner membrane.

During this process, for each pair of electron being transported to ubiquinone from $NADH$ through $FMN$ and $Fe-S$ center, complex I pumps four protons into the inner membrane space.

Final answer:

(C) Four