Question
Which substance acts as the best buffer against acid rain?

Conclusion
My hypothesis was correct – milk of magnesia did serve as the best buffer against acid rain out of the 3 substances. However, do I think farmers should use this to protect their crops from harmful acid rains? No, probably not. Although it did end up counteracting the acid, the thickness of the milk of magnesia ended up choking the leaves of the plant. Wherever the solution was poured on the leaves, it would create a brown dead spot that grew until it eventually took over the whole leaf. Unless you are extremely careful when watering the plant, accidentally dribbling some of the substance onto the leaves is practically inevitable, so you would most likely damage some of the plant. So in conclusion, the milk of magnesia did do its job of nullifying the effects of acid rain, but it ended up creating some completely different problems of its own.
Another part of my hypothesis was correct in that the ammonia was in fact harmful to the plant. It was too strong of an alkaline liquid for the plants to handle, even with the acidity of the acid rain.
However, something that surprised me was the effect of the baking soda solution on the plants. These plants seemed to die even faster than the ones being watered with just the acid rain. I thought that the acid rain would be counteracted to some extent by the baking soda, but not quite enough since the baking soda solution had a pH of 9, not 10. But that definitely wasn’t the case; the baking soda killed the plants rather than even somewhat protecting them. I am still unsure as to why this happened. I have a theory that it occurred because the plants reacted not only to the pH of the solution, but to chemical makeup of the baking soda as well. It’s a question that requires further research and experimentation.
Observations
1/31
The experiment has not started yet (will begin February 2).
All plants are in good health, except for a couple nicks and brown spots here and there.
2/2
The experiment began today, so naturally, the plants are in still in good health, and basically nothing changed.
2/4