For a good burning kerosene that meets clean-combustion expectations, the smoke point measured in a standard lamp typically lies around which range (in mm): 0–5, 20–25, 60–75, or 100–120?

Introduction / Context:
Smoke point is a standardized indicator of a kerosene’s tendency to form soot. It is reported as the maximum flame height, in millimetres, at which a standard test flame burns without visible smoke. Higher smoke points correspond to lower aromatic content and cleaner burning, which is vital for illuminating kerosene and aviation turbine fuel specifications.

Given Data / Assumptions:

• Measurement: millimetres of smokeless flame height in a standardized lamp.
• “Good burning” kerosene implies meeting typical commercial specification minimums.
• Room conditions and procedure follow the standard method.

Concept / Approach:
Commercial illuminating kerosenes and aviation kerosenes generally target smoke points around the low-to-mid 20s mm to ensure clean combustion. Significantly lower values (e.g., 0–5 mm) would indicate extremely poor burning quality, while very high values (60–120 mm) are unrealistic for normal kerosene fuels under standard test conditions.

Step-by-Step Solution:

Verification / Alternative check:
Fuel standards and product datasheets frequently cite smoke point minima near 20–25 mm for clean-burning grades, particularly to control visible smoke in lamps and reduce soot formation in burners.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing smoke point with flash point or freezing point; these measure different properties (safety and low-temperature operability respectively).

Final Answer:
20–25