When NADH passes its electrons to the electron transport chain (ETC), it is oxidized.

Here's why:

* NADH is a reduced form of NAD+. It carries a hydride ion (H-) and two electrons.

* The ETC accepts electrons. This process removes the electrons from NADH, leaving it in its oxidized form, NAD+.

* Oxidation is the loss of electrons.

In summary: NADH donates its electrons to the ETC and becomes oxidized to NAD+.