Correct Option
The correct option is
1 and 3 only
Explanation
The chemical properties of combustion, specifically the conditions required for flame formation, the nature of combustible substances, and the comparative calorific values of common fuels.
Statement-wise Analysis
- Statement 1 is Correct. Magnesium is a reactive metal. When heated, it burns in air with a dazzling white flame to react with oxygen, forming Magnesium Oxide ($2Mg + O_2 \rightarrow 2MgO$).
- Statement 2 is Incorrect. A substance produces a flame during combustion only if it vaporizes. Charcoal does not vaporize upon heating; it burns by glowing red but does not produce a flame. In contrast, substances like wax or kerosene vaporize and thus form flames.
- Statement 3 is Correct. Kerosene oil is a combustible substance that catches fire readily. While technically distinguished from highly "inflammable" substances (like petrol) by ignition temperature in strict scientific definitions, in the context of general classification of fuels, it is correctly identified as a substance that burns.
- Statement 4 is Incorrect. The calorific value indicates the efficiency of a fuel. The calorific value of Wood is approximately 17,000–22,000 kJ/kg, whereas Coal has a higher calorific value ranging from 25,000–33,000 kJ/kg. Thus, wood has a lower calorific value compared to coal.
Key Takeaway
Flame Formation: Only substances that vaporize during burning produce a flame (e.g., Wax, Kerosene). Substances that do not vaporize (e.g., Charcoal) only glow.