Final answer:
Aluminum chloride in its solid form (AlCl₃(s)) is the substance with a definite shape and definite volume at STP, as solids possess both of these physical properties.
Step-by-step explanation:
The student has asked which substance has a definite shape and a definite volume at Standard Temperature and Pressure (STP). Of the options provided, AlCl₃(s), or aluminum chloride in its solid form, has a definite shape and volume. This is because solids are characterized by having fixed shapes and volumes.
Comparatively, NaCl(aq) represents sodium chloride in an aqueous solution, which means it is dissolved in water and therefore does not have a definite shape, although it does have a definite volume. Cl₂(g) represents chlorine gas, which has neither a definite shape nor a definite volume, as gases fully expand to fill their container. CCl₄ is carbon tetrachloride, which, if not specified, is commonly a liquid at room temperature and thus would have a definite volume but not a definite shape.