Which of the following cell organelle is mainly involved during apoptosis?

Loss of mitochondrial function is seen during apoptosis. Mitochondrial membrane integrity is not maintained, causing the end of normal activity and release of cytochrome c into the cytoplasm where it activates proteolytic enzymes called caspases. The initial caspases activate a cascade of other caspases, resulting in protein degradation throughout the cell. Ref: Mescher A.L. (2010). Chapter 3. The Cell Nucleus. In A.L. Mescher (Ed), Junqueira's Basic Histology: Text & Atlas, 12e.