Final answer:
Fluids like liquids have a definite volume but no fixed shape, merging into the shape of their containers, whereas gases have neither a fixed shape nor a definite volume. Crystals, being solid, have both a definite shape and volume.
Step-by-step explanation:
The question at hand is regarding the physical characteristics of fluids versus crystals, specifically in terms of shape and volume. According to the principles of chemistry and physics, solids, including crystals, have a definite shape and a specific volume, which means they maintain their form regardless of the container they are in. In contrast, liquids and gases do not have a fixed shape but have different volume characteristics. Liquids have a definite volume but take the shape of the container holding them. Gases, however, have neither a definite volume nor shape, as they expand to fill their container entirely. Given the provided choices, the accurate statement would be that a fluid has an indefinite shape but a definite volume when it comes to liquids, and an indefinite shape and volume concerning gases, while crystals (solids) have both a definite shape and volume.