During electron transport system (ETS), electron transport proceeds from carriers that have _____ redox potential to those having _____ redox potential. This electron transport down to the energy gradient leads to the formation of ATP from ADP and Pi, which is referred to as_______.

Assertion (A): When electrons move through the transport chain, protons are transported across the membrane.

Reason (R) : Because the primary acceptor of electron located towards the outside of the membrane, transfers its electrons to a H carrier (PQ). 

The correct option among the following is:

The correct match is:

Arrange the given reactions occur in electron transport in correct sequence.

$I)$ Oxygen $\to$ Removes ${\mathrm{H}}_2$ from ETS $\to$ Receives electrons form $ETS$.

$II)$ Ubiquinone $\to$ Oxidized from ubiquinol $\to$ Receives reduced equivalents from ${\mathrm{FADH}}_2$.

$III$Cyt C oxidase $\to$ Reduced by cytochrome $\mathrm{C}\to$ Electron donor for ${\mathrm{O}}_2$ to release ${\mathrm{H}}_2\mathrm{O}$.

$IV)$ Cytochrome $\mathrm{C}\to$ Mobile carrier $\to$ Transfer $e^{-}$ from cyt $\mathrm{b}$ to cyt $\mathrm{c}$ oxidase.