Final answer:
Liquids are incompressible due to the close proximity of their molecules, while gases are compressible because they have more space between molecules and can be squeezed closer together under pressure. So, the best answer is a, Liquids are incompressible; gases are not.
Step-by-step explanation:
The substances that are incompressible and those that are not can be identified by understanding the properties of liquids and gases.
According to physics, liquids are essentially incompressible; they do not significantly change volume when pressure is applied.
This is because the molecules in a liquid are close together and there is very little space between them.
On the other hand, gases are compressible because there is a lot of space between the molecules, and they can be squeezed closer together when pressure is increased.
Therefore, the correct answer to the student's question is: a) Liquids are incompressible; gases are not.
The distinguishable behavior of liquids and gases under compression is due to their molecular structure. While gases can undergo large volume changes as pressure changes, liquids cannot.
Consequently, this characteristic makes gases able to compress and expand to fill the space they are in, while liquids maintain a consistent volume regardless of the shape of their container.
So, the best answer is a, Liquids are incompressible; gases are not.