~choices below~bob was investigating chemistry one morning trying to learn the differences between chemical and physical properties. what can you tell him about how chemical properties of a substance differ from physical properties? a) physical properties can be observed without changing the identity of the substance, while chemical properties cannot. b) tools are needed to measure chemical properties, but not physical properties. c) chemical properties can be used to identify a substance, but physical properties cannot. d) all physical properties can be observed, while chemical properties cannot.