Answer:
Option D, oxidized
Explanation:
The NADH gets oxidised when it passes its electrons into the Electron Transport System
Oxidization is a process in which one element or compound loses its electron to other chemical element or compound thereby itself getting oxidised and reducing the other one (the one who gains the electron).
Here in the electron transport system, the NADH loses or donates its electron to the Electron Transport System thus chemically it gets oxidized.
Hence, option D is correct
