Identify the correct sequence of cytochromes involved in ETS.

In the electron transport system (ETS), electrons are transferred from ubiquinol to cytochrome $c$ via the cytochrome $bc_1$ complex (Complex III).

Cytochrome $c$ is a small protein attached to the outer surface of the inner mitochondrial membrane and acts as a mobile carrier for the transfer of electrons between Complex III and Complex IV.

Complex IV refers to the cytochrome $c$ oxidase complex containing cytochromes $a$ and $a_3$, along with two copper centers.

Thus, the correct sequence of electron transfer through the cytochromes is $C_y t\ bc_1 \rightarrow C_y t\ C \rightarrow C_y t\ a \rightarrow C_y t\ a_3$.

Answer: $C_y t\ bc_1 \rightarrow C_y t\ C \rightarrow C_y t\ a \rightarrow C_y t\ a_3$