This is concerned with the intrinsic pathway of apoptosis

The correct option is cytochrome c.

Apoptosis, or programmed cell death, can be initiated via two main pathways: the extrinsic (death receptor) pathway and the intrinsic (mitochondrial) pathway.
The intrinsic pathway is triggered by intracellular stress signals, such as DNA damage, oxidative stress, or severe cellular damage.

In response to these stress signals, pro-apoptotic proteins of the Bcl-2 family (such as Bax and Bak) become activated and insert themselves into the outer mitochondrial membrane.
This insertion causes mitochondrial outer membrane permeabilization (MOMP), creating pores that allow the release of mitochondrial proteins into the cytosol.

Among these released proteins, cytochrome c is the critical mediator.
Once in the cytosol, cytochrome c binds to an adaptor protein called apoptotic protease activating factor-1 (Apaf-1) in the presence of dATP or ATP.
This binding induces the oligomerization of Apaf-1 into a heptameric wheel-like protein complex known as the apoptosome.

The apoptosome then recruits and activates the initiator caspase, procaspase-9, converting it to active caspase-9.
Active caspase-9 subsequently cleaves and activates executioner caspases (such as caspase-3 and caspase-7), leading to the systematic dismantling and death of the cell.
Therefore, cytochrome c is the key mitochondrial component uniquely involved in propagating the intrinsic apoptotic signal.