The correct option is (b).
Explanation
Fire extinguishing relies on the principle of cutting off the oxygen supply or reducing the temperature of the fuel below its ignition point. The effectiveness of an extinguishing agent depends on its physical properties, particularly density, relative to the fuel.
Statement-wise Analysis:
- Statement 1 is Incorrect: Water is not effective for extinguishing oil or petrol fires. It does not form a protective blanket over the oil. To extinguish a fire by "blanketing," the agent must float on top of the fuel to separate it from oxygen. Since water does not float on oil, it cannot perform this function.
- Statement 2 is Correct: Water is denser (heavier) than oil and petrol. When water is poured onto an oil fire, it sinks below the oil layer. Consequently, the oil floats on top of the water and continues to burn as it remains in contact with atmospheric oxygen. Furthermore, the intense heat can cause the water to flash-boil into steam, potentially splashing the burning oil and spreading the fire.
Key Takeaway:
Water is unsuitable for extinguishing fires involving flammable liquids (Class B fires) like oil and petrol because it is denser than the fuel; it sinks to the bottom, allowing the fuel to float and continue burning.