Junior high school physics problems

The upward buoyancy of the air on the balloon in the air = air density * balloon volume *g= 103.2N, the downward force 9 * *10 = 90n, and the force pulling it = 103.2-90 = 65438.

B.

Aluminum has the lowest density, the same mass and the largest volume, all of which sink to the bottom of the water, so the liquid volume displaced by aluminum is the largest, so the height of water rising is the largest. According to the formula, the pressure of this water on the bottom of the cup increases the most.