Which temperature air would have the lowest pressure? (assuming all other factors are constant) a 100 degrees F
b 75 degrees F
c 50 degrees F
d 25 Degrees F

I believe it would be D because as temperature decreases so does pressure

When temperature increases then the pressure increases and when the temperature decreases, so does the pressure. So your answer would be 25 Degrees.

By water evaporation from the leaves is created a negative pressure at the top of the tree that promotes the ascension  of the water through channels that are called xylem. there are also two molecule forces that are involved: the intra-water molecules cohesion (water molecules stick to each other) and the adhesion when the water molecules stick to the channels they are running in. this is what enables water to go from the roots to the top of a tall tree.