Which shows a situation where the physical and chemical properties of substances have not changed?
Chemical properties change if molecules themselves change, i.e., if molecules bond to form other molecules or break down to form simpler ones. Physical properties change when the state is changed (among other changes).
Let us analyze each situation in the attached images:
a) The reactant molecules dissociate and form new (i.e. different) molecules as the product, hence both properties will be different.
b) Similar to case (a), the reactant and product molecules are different, hence will have different properties.
c) Two liquids are mixed, and we end up with some solid particles in the liquids. Here, precipitation has happened resulting in solid particles. Since a state change has taken place, physical properties will be different.
d) Here, we start with solid particles in a liquid medium, and we have dispersal of solid particles throughout the liquid. This is the scenario where we can say that chemical and physical properties are the same and have not changed in reactants and products.