Electron transport system occurs in $:-$

Where does oxidative phosphorylation occur?

The oxidation of one $NADH_2$ yields (in $ATP$)

Given below are two statements.
Statement-$I$: Cytochrome $c$ is a small, copper-containing protein loosely attached to the inner membrane.
Statement-$II$: Cytochrome $c$ acts as a mobile electron carrier transferring electrons between complex $I$, $II$, and $IV$.
In the light of the above statements, choose the correct answer from the options given below.

Cytochromes are defined as:

The main purpose of the electron transport chain is to