Which complex in the ETC accepts electrons from NADH via an FMN cofactor?

The correct choice is indeed Complex I, also known as NADH:ubiquinone oxidoreductase. This complex initiates the electron transport chain (ETC) by accepting electrons from NADH, which is generated during metabolic processes such as glycolysis and the citric acid cycle.

Complex I contains a flavin mononucleotide (FMN) cofactor that plays a crucial role in the first step of this electron transfer. When NADH binds to Complex I, FMN is reduced to FMNH2 as it accepts two electrons from NADH. The electron transfer through Complex I is coupled with proton pumping from the mitochondrial matrix to the intermembrane space, contributing to the proton gradient that drives ATP synthesis.

Unlike Complex I, Complex II (succinate dehydrogenase) accepts electrons from succinate and does not utilize FMN; instead, it features a cofactor called FAD. Complex III (cytochrome bc1 complex) accepts electrons from ubiquinol and serves to transfer them to cytochrome c. Lastly, Complex IV (cytochrome c oxidase) is the final electron acceptor in the chain, reducing oxygen to water. Thus, the unique role of FMN and the specific electron source