Typical quality of commercial petrol (gasoline): The general octane number range of petrol commonly available for road use is approximately

Introduction / Context:
Octane number measures a spark-ignition fuel’s resistance to knock. Road gasoline is sold with octane ratings (often Research Octane Number or combined pump octane) tuned for typical passenger engines. Recognising common ranges aids in proper fuel selection and knock diagnostics.

Given Data / Assumptions:

• Regular and premium petrol grades on retail forecourts.
• Octane presented as RON (common outside North America) or (R+M)/2 as “pump octane”.
• Question seeks a broad, commonly encountered range.

Concept / Approach:

Regular petrol is typically around RON 91–95; premium can be RON 95–99+ depending on market. The composite pump octane is slightly lower but still aligns within an approximate 80–100 span internationally for ordinary road fuels.

Step-by-Step Solution:

Verification / Alternative check:

Automaker owner’s manuals commonly recommend fuels within this band, and forecourt labels corroborate the values.

Why Other Options Are Wrong:

20–80 are unrealistically low for modern road petrol; 100–120 exceeds typical pump grades and enters racing/special fuels territory.

Common Pitfalls:

Confusing RON with MON or (R+M)/2; overlooking regional labeling differences while the practical range remains similar.

Final Answer:

80 to 100