Inner membrane of mitochondria is rich in phospholipid _______

The correct option is cardiolipin.

To understand why cardiolipin is the correct answer, let's look at the structure and composition of the inner mitochondrial membrane:
1. Unique Lipid Composition: Unlike most other biological membranes, the inner mitochondrial membrane (IMM) has a highly specialized lipid profile necessary for its role in energy production (ATP synthesis via the electron transport chain).
2. What is Cardiolipin? Cardiolipin (diphosphatidylglycerol) is a double phospholipid containing four fatty acid tails instead of the usual two. This unique dimeric structure allows it to form a conical shape, which helps in the curvature of the membrane (forming the cristae) and stabilizes the respiratory chain complexes.
3. Abundance in IMM: Cardiolipin constitutes about 20% of the total lipid composition of the inner mitochondrial membrane. It is synthesized locally within the mitochondria and is essential for the optimal functioning of enzymes involved in cellular respiration.

Thus, the inner membrane of mitochondria is rich in the phospholipid cardiolipin.