The thickness of the outer mitochondrial membrane, which encloses the entire organelle, is 60 to 75 angstroms $\left(Å\right)$ . It has a protein-to-phospholipid ratio similar to that of the cell membrane (about 1:1 by weight). It consists of a large number of porins, an integral membrane proteins. The pore-forming voltage-dependent anion channel is the major trafficking protein.
The inner membrane of mitochondria has convoluted foldings.
The inner membrane encloses the matrix. It consists of 2/3 of the total protein in a mitochondrion. The matrix is important in ATP synthesis with the aid of the ATP synthase contained in the inner membrane. The matrix contains a highly concentrated mixture of hundreds of enzymes, special mitochondrial ribosomes, tRNA, and several copies of the mitochondrial DNA genome. Therefore, 2 is the answer.