Answer
a. above
b. III
Work Step by Step
a.
Let there be n drops free falling in midair, counting as 1 being the closest to the floor. The n-th drop has just begun to fall. The drop before it has been in freefall for $\Delta t$, while drop 1 has been freefalling for a time $(n-1)\Delta t.$
Because distance increases with the square of time, the drops at the bottom are farther apart than the ones at the top. So, in the column of n drops, there are more drops in the upper half than in the lower half. Assuming drops are identical in mass, and since there are more of them in the upper half, we expect the center of mass to be above the halfway distance to the floor.
b.
I: the drops do not bunch; they are in free fall.
II: no, they are not evenly spaced as they fall. The ones falling for a longer time are farther down.
III: this is the best explanation
