ANS:C - maximum height of flame (in mm) without causing smoking, when burnt in a standard lamp.

The smoke point of kerosene refers to the maximum height of flame (in millimeters) that can be achieved without causing smoking when the kerosene is burnt in a standard lamp. So, the correct option is:

• Maximum height of flame (in mm) without causing smoking, when burnt in a standard lamp.

The "maximum height of flame (in mm) without causing smoking" is a parameter used to characterize the quality of kerosene or other liquid fuels when burned in a standard wick lamp or burner. Here’s a detailed explanation:

1. Standard Wick Lamp: A standard wick lamp is a device used to burn kerosene or similar liquid fuels. It typically consists of a wick that draws fuel from a reservoir and burns it to produce light and heat.
2. Smoke Formation: When a fuel like kerosene burns inefficiently or incompletely, it can produce smoke. Smoke formation occurs when the combustion process is not optimal, often due to factors such as incomplete mixing of fuel and air, poor fuel quality, or improper adjustment of the burner.
3. Measurement: To assess the quality of kerosene or its suitability for use in lamps:
   • The kerosene is burned in a standardized setup.
   • The height of the flame is carefully monitored.
   • The maximum height of the flame that can be sustained without producing visible smoke is recorded.
4. Importance: The maximum height of flame without smoke is an important indicator of fuel quality and combustion efficiency. Higher quality kerosene or cleaner-burning fuels will produce a taller flame without smoking, indicating more complete combustion and fewer emissions of soot and particulate matter.
5. Application: This parameter is used in various contexts, including:
   • Household Use: Ensuring that kerosene used in lamps does not produce excessive smoke, which can lead to indoor air pollution and health issues.
   • Industrial Applications: Assessing the suitability of fuels for burners and combustion processes where smoke emissions need to be minimized for environmental or operational reasons.

In summary, the maximum height of flame without causing smoking is a practical measure used to evaluate the cleanliness and efficiency of kerosene or similar fuels when burned in standard lamps. It helps ensure optimal combustion and minimal environmental impact during use.