I am pretty sure my answer was right but the online test said that it is wrong.

The amount of energy stored in a plant through photosynthesis could be estimated best by

A) taking the mass of the plant before and after

B) taking the mass of the water consumed by the plant

C) determining the amount of carbon dioxide consumed

D) determining the amount of oxygen produced.

Incorrect. Your answer=D, Correct answer=A

remember for that every time an electron passes through the electron transport chain the
amount of atp produced is 32 units and the amount of oxygen produced is one unit so if
you determine the amount of oxygen produced you should be able to tell how much
energy is produced right?

I think d is wrong because it would be very difficult to calculate the amount of oxygen produced and there is a chance that the oxygen could react before it is tested. Also how could you ensure you would be testing in an environment the would be free of all oxygen other then that produced in the reaction.
My bio teacher once told me "muliple choice is not about the one right answer and the 3 wrong but the answer that is most correct". A is the most correct because both the byproducts of photosynthesis (water and oxygen) are relseased as gases so the only mass left would be the glucose (energy) so it would be the weight diference between the two plant measurements.

I agree with bounddragon, though the question itself is a bit ambiguous. It says 'estimate', so, A, C and D are relatively acceptable. But since the best estimation is required, it is easier to carry out experiment in A. Gases are pretty difficult to deal with, just think about how you would collect the oxygen, like you suggested. Say you succeeded in collecting all oxygen released, then, what about the carbon dioxide the plant needs? Do you realise what I mean?

It's definitely not B.
C could work since photosynthesis is the fixing of carbon. But measuring how much carbon was fixed is the question. "Consumed" is too vague. If they just mean how much CO2 went into the stomata, then C is wrong. Same argument for oxygen.

A would be correct, I think, IF you specify dry mass. If you include gain in water it's wrong. And of course there's no way to take the dry weight of a plant and then have it photosynthesize because you've killed it. You'd have to have hundreds of plants and take the dry weight of a random sample of them before and after. The answer as written does NOT specify dry weight and so is technically wrong.

( It's also not strictly true that photosynthesis generates 32 ATP molecules. It depends on the situation. It can vary and the numbers aren't round, strangely. But most teachers and textbooks avoid that topic!)

I think it's a dumb, badly written question if that's any comfort.

I think the question is stupid too, it would be better if it was a short answer and not a multiple choice, I think the question does not have a strickly right answer but is designed to test the understanding of the individual

Thank you

I personally think that the test is correct and unfortunately you are wrong. This is because the amount of oxygen produced is not the amount of energy that the plant has aquirred through photosynthesis - instead it is just a fraction of that energy. Before the plant produces oxygen it also needs to use the energy from photosynthesis to perform growth and respiration etc.
Hope this helps.