Please answer and explain the question in the image

Ascience research group is testing a new type of plant food. one trial is conducted in a controlled experiment. the data from the trial show that the plant that received the new food grew faster than the control plant. the group announces that the new plant food makes plants grow faster. what is the main weakness in this scientific claim?

This is the interaction of two organisms where one is and the other is neither nor harmed.

Vinegar has a ph of 3, and household ammonia has a ph of 11. is the concentration of h+ greatest in the vinegar or ammonia?