Correct Option
The correct option is (a).
Explanation
The fundamental distinction between physical changes and chemical changes. A physical change involves a transformation in the state or appearance of matter without altering its chemical composition, whereas a chemical change results in the formation of new substances through chemical reactions.
Statement-wise Analysis
- Statement 1 is Correct: Liquified Petroleum Gas (LPG) consists mainly of butane and propane. It is stored in cylinders under high pressure, which keeps it in a liquid state. When the valve is opened, the pressure is released, causing the liquid to vaporize and convert into a gas. This is a phase transition.
- Statement 2 is Incorrect: The burning of LPG is a chemical change (combustion), not a physical change. During combustion, the hydrocarbon gas reacts with oxygen in the air to produce carbon dioxide, water vapour, and heat. Since new substances are formed and the process is irreversible, it is a chemical change.
- Statement 3 is Incorrect: The transition of LPG from a liquid state to a gaseous state is a physical change. In this process, only the physical state of the substance changes (from liquid to gas) due to a change in pressure, but the chemical composition (molecular structure of butane/propane) remains identical.
Key Takeaway
Phase transitions (like vaporization or melting) are physical changes because the chemical identity remains unchanged. Combustion (burning) is a chemical change because it involves oxidation and the creation of new chemical products.