Which of the following is not a fluid?
a. compressed
b. air
c. oil
d. dry cement alcohol

Dry cement

Explanation:

Matter can be in three different states: solids, liquids or gases. Liquids or gases are also called 'fluids'. The main difference between solids and fluids is:

- in solids, the molecules are bond together, and so they cannot move freely inside the substance, but they can only vibrate around their position. For this reason, solids have a well-defined shape and they occupy a well-defined volume.

- in fluids, the molecules are NOT bond together, and so they are free to move. For this reason, fluids do not have a well defined shape or volume, but they tend to occupy the volume of their conteiner.

Among the choices given, we see that air, oil and alcohol respect the conditions listed for fluids, so they are fluids; on the contrary, dry cement respects the conditions listed for solids, so it is a solid.