A piece of iron sinks to the bottom of a lake where the pressure is 21 times what it is at the surface of the lake. Which statement best describes what happens to the volume of that piece of iron?A. There has been no change in the volume of the iron.
B. Its volume decreases slightly.
C. Its volume becomes 21. times greater.
D.Its volume increases slightly.

In real life, applying to solid will shrink it depending on the amount of pressure applied, but due to the strength of solid bonds, the volume change is often negligible in practical situation and would only be accounted under astronomically high pressure phenomena (eg. at Jupiter's core or near black hole).

In high school level, and for many applications, it is entirely viable to completely neglect the change in solid volume under pressure. Thus, A is a legitimate answer. However, bear in mind that in theory the volume still decreases by a very slight amount. So B is correct as well, theoretically. The most correct option depends on the precision you needed.