How many electrons must get passed down the Electron Transport Chain before energy is generated?

4 electrons

Explanation:

Electron transport chain is defined as the series of process in which electron transfer takes place across a membrane. It is consists of enzymes, peptides, and other molecules.

There are 4 electrons that passed down the Electron Transport Chain before energy is generated. These Four electrons further reduce each molecule of oxygen. Oxygen binds with free proton and form water and move across the membrane to form ATP.

Hence, the correct answer is "4 electrons".

Leonardo da Vinci studied rocks and fossils in order to determine that the Earth and the entire world is actually so much older than the Genesis (from the Bible) suggests. He wanted to disprove the belief taught by the Bible that the Earth was created when God created it - he used his science to prove Bible wrong, and his study is still relevant even today.