Electron transfer translocates protons from the mitochondrial matrix to the external medium

Electron transfer translocates protons from the mitochondrial matrix to the external medium. The tendency of protons to diffuse back into the matrix is the driving force for ATP synthesis by ATP synthase. During oxidative phosphorylation
by a suspension of mitochondria in a medium of pH 7.4, what would you predict the pH of the matrix to be?

a. 8.0

b. 6.8

c. 7.4