Final answer:
The property of substances that can help you sort them into different groups are solubility and composition. Reactivity is not a property that can be used for sorting substances.
Step-by-step explanation:
The property of substances that can help you sort them into different groups are as follows:
a) Salt and sugar: Solubility
b) A piece of granite and rocksalt: Composition
c) Solubility, composition, and density are all properties that can help classify substances into different groups. However, reactivity is not a property that can be used for sorting substances.