Final answer:
The characteristics of the unknown substance can be classified as physical or chemical properties based on their observability or ability to undergo a chemical change.
Step-by-step explanation:
The observation that the substance is brittle is a physical property. Physical properties are characteristics of a substance that can be observed or measured without changing its identity. In this case, the brittleness of the substance can be observed without changing its chemical composition.
The observation that the substance is a dull, grey solid is also a physical property. The color and state of matter are both physical properties that can be observed without changing the substance's identity.
The observation that the substance reacts with bromine to give a powdery, yellow solid is a chemical property. Chemical properties describe the ability of a substance to undergo a specific chemical change. In this case, the reaction with bromine indicates a chemical change.
The observation that the substance melts at 120 °C and boils at 452 °C are both physical properties. The melting and boiling points of a substance are characteristic physical properties that can be measured without changing the substance's identity.
The observation that the substance is a poor conductor of electricity is a physical property. Electrical conductivity is a physical property that can be observed without changing the substance's identity.
The observation that the substance burns in air, producing a bright blue light, is a chemical property. The ability to burn and produce a flame is a characteristic chemical property of certain substances.
The observation that the density of the substance is 2.085 g/cm³ at 20°C is a physical property. Density is a physical property that can be measured without changing the substance's identity.