Explain why the suspension of isolated chloroplasts became alkaline when illuminated?

Yes, protons are pumped across the membrane, but flow right back again through the ATP synthase.  More important is that illumination is required for carbon fixation.  As photosynthesis runs, the chloroplasts remove CO2 from the water they are suspended in.  In solution, CO2 forms carbonic acid, so removing CO2 will reduce the level of carbonic acid, raising the pH.

Explanation:

your answer should be c) enjoy!