The pH of the inner thylakoid space has been measured, as have the pH of the stroma and of the cytosol of a particular plant cell. Which, if any, relationship would you expect to find?
a. the pH within the thylakoid is less than that of the stroma
b. there is no consisten relationship
c. the pH of the stroma is lower than that of the other two measurements
d. the pH of the stroma is higher than that of the thylakoid space but lower than that of the cytosol

a. the pH within the thylakoid is less than that of the stroma

Explanation:

The pH of thylakoid membrane is 8 at normal conditions but it became highly acidic like 4 during photosynthesis. The electron transport chain utilize the energy released by excited electrons to pump the H+ ions to lumen of thylakoid membrane from stroma during light reaction of photosynthesis. The H+ ions are present in both the stroma and thylakoid membranes. These high potential H+ ions are utilized by ATP synthase complex for the production of ATP.

We know that more the H+ ions lesser will be the pH and lumen have the high concentration of H+ ions. While the pH of stroma is normally kept acidic by plants to create a concentration and potential difference of H+ ions for the production of ATP. That why the lumen have lower pH than stroma of chloroplast.

A.the pH within the thylakoid is less than that of the stroma

Explanation:

Hydrogen atom is constantly been transported into the stroma by  the NADPH2 from Kreb Cycle; and  constantly splits into Protons and  Electrons.

The electrons forms a chain of transport mechanism,(ETC) which generate  pumping energy   called Proton Motive Force.

The PMF  continuously pumps  protons into the thylakoid space, (thylakoid intramembranes)setting up electrochemical gradients.This lowers the pH, increases  the acidity of the thylakoid and thylakoid space compare to the stroma.