Correct!

What cellular compartment becomes acidic (high concentration of hydrogen ions) during mitochondrial electron transport?

A. mitochondrial stroma

B. cytoplasm

C. endoplasmic reticulum

D. space between inner and outer mitochondrial membranes

Electron transport produces a high concentration of H⁺ (protons) in the inner membrane space of the mitochondria.

E. thylakoid membranes