The correct option is (a).
Explanation
The mechanism of a modern safety matchstick relies on separating the combustible components from the ignition initiator to ensure safety. The chemical reaction is triggered by friction, which generates enough heat to initiate combustion between the fuel and the oxidizer.
Analysis of Chemicals:
- 1. Antimony trisulphide (Correct): This chemical is present in the head of the matchstick. It functions as the primary combustible fuel that burns to produce the flame.
- 2. Potassium chlorate (Correct): This chemical is present in the head of the matchstick. It acts as a strong oxidizing agent, providing the oxygen required to burn the antimony trisulphide rapidly.
- 3. White phosphorus (Incorrect): White phosphorus was used in early matchsticks but was highly toxic and caused severe health issues (such as "phossy jaw") for industrial workers. It is not used in modern safety matches.
- 4. Red phosphorus (Incorrect): While essential to the mechanism, red phosphorus is not present in the matchstick head. It is applied to the rubbing surface on the side of the matchbox, mixed with powdered glass. Friction converts a small amount of red phosphorus into white phosphorus, which then ignites the chemicals in the match head.
Key Takeaway:
The head of a modern safety match contains a mixture of antimony trisulphide and potassium chlorate, whereas the rubbing surface contains red phosphorus and powdered glass.