The correct option is 3 and 4 only.
Explanation
Properties of matter are broadly classified into physical and chemical properties. This classification depends on whether the observation of the property involves a change in the chemical identity of the substance. Physical properties can be observed or measured without changing the substance's composition, whereas chemical properties describe the ability of a substance to undergo a specific chemical change.
- Statement 1 is Incorrect: Melting point is a physical property. It is the temperature at which a solid becomes a liquid. This transition is a change of state (phase change) and does not alter the chemical composition or identity of the substance.
- Statement 2 is Incorrect: Boiling point is a physical property. It is the temperature at which a liquid turns into a vapor. Similar to melting, boiling involves a physical change of state without any chemical reaction or modification of the molecular structure.
- Statement 3 is Correct: Acidity is a chemical property. It defines a substance's ability to act as an acid (donating protons or accepting electron pairs) during a chemical reaction. It describes the chemical behavior of the substance in relation to other substances.
- Statement 4 is Correct: Reactivity with acids is a chemical property. It refers to the tendency of a substance to undergo a chemical reaction with an acid, resulting in the formation of new substances (products). This process involves the breaking and making of chemical bonds.
Key Takeaway: Physical properties (e.g., density, color, melting point, boiling point) relate to the physical state or appearance, while chemical properties (e.g., flammability, toxicity, acidity, reactivity) describe how a substance behaves during a chemical reaction.