The correct option is (a).
Explanation
In chemistry and safety standards, substances are classified based on their ignition temperature. Inflammable substances are defined as those that have a very low ignition temperature and can easily catch fire with a flame. While many substances are combustible (capable of burning), only those with low ignition temperatures and high volatility are categorized as inflammable.
Statement-wise Analysis:
- 1. Petrol: Correct. Petrol is a highly volatile liquid mixture of hydrocarbons. It has a very low flash point and ignition temperature, making it a classic example of an inflammable substance.
- 2. Alcohol: Correct. Alcohols (such as ethanol) are volatile organic compounds with low ignition temperatures. They vaporize readily and catch fire easily upon contact with a flame.
- 3. Liquified Petroleum Gas (LPG): Correct. LPG is a mixture of hydrocarbon gases (primarily propane and butane). It is stored under pressure as a liquid but vaporizes immediately upon release. It has a very low ignition temperature and is highly inflammable.
- 4. Charcoal: Incorrect. Charcoal is a solid fuel obtained from carbonization. While it is a combustible substance (it can burn), it does not have a "very low" ignition temperature compared to volatile liquids or gases. It generally requires significant heating to reach its ignition point and often burns without a flame (glowing combustion), distinguishing it from substances strictly classified as inflammable in safety contexts.
Key Takeaway:
The primary distinction between general combustible substances (like wood or charcoal) and inflammable substances (like petrol, alcohol, and LPG) is that the latter have very low ignition temperatures and ignite readily with a flame.