Final answer:
The pressure at the base of the drum decreases when taken from Earth to the lunar surface due to the weaker gravitational force.
Step-by-step explanation:
When a drum filled with water is taken from the Earth to the lunar surface, the pressure at the base of the drum decreases. This is because the pressure at the base of the drum is equal to the weight of the water above it divided by the area of the base. On the Earth, the weight of the water is greater due to the gravitational force, resulting in a higher pressure compared to the lunar surface where the gravitational force is weaker.