Final answer:
Water has a different physical state at room temperature compared to salt, sugar, and flour, as it is liquid while the others are solids. Fluids at room temperature include air and water as gases, and mercury as a liquid. Gases are easier to compress because their particles are further apart than those in liquids or solids.
Step-by-step explanation:
The student has asked which substance has a different physical state at room temperature compared to salt, sugar, and flour. To answer this, we should be aware of the typical states of matter of these substances. Salt, sugar, and flour are all solids at room temperature. However, water is a liquid at room temperature, unlike the other substances listed which are solids. Thus, water has a different physical state at room temperature compared to salt, sugar, and flour.
Moreover, to address the conceptual questions, it is important to note that fluids can be either gases or liquids and they are distinguished from solids by their ability to flow and conform to the shape of their containers. The substances among air, mercury, water, and glass that are fluids at room temperature are air (gas), mercury (liquid), and water (liquid). Glass is a solid and therefore is not considered a fluid. Gases are easier to compress than liquids and solids because the particles in a gas are much further apart than those in liquids and solids, allowing them to be brought closer together more easily. Gases differ from liquids mainly in that they have neither a definite volume nor shape, whereas liquids have a definite volume but no definite shape.