ANS:A - sulphur stick, which on detection gives white smoke.

A sulfur stick, also known as a sulfur candle or sulfur dioxide generator, is a device used to detect leaks in gas pipelines, refrigeration systems, or other enclosed spaces. The sulfur stick contains a mixture of sulfur and other substances that produce sulfur dioxide (SO2) gas when ignited. Here's how it works:

1. Composition: The sulfur stick consists of a small, cylindrical container filled with a mixture of sulfur powder and other combustible materials. These materials are chosen to ensure consistent and controlled combustion when the stick is ignited.
2. Ignition: To use the sulfur stick, it is typically ignited by lighting the end of the stick with a flame, similar to lighting a candle. Once ignited, the sulfur stick begins to burn, releasing sulfur dioxide gas into the surrounding environment.
3. Detection: If there is a leak in a gas pipeline or refrigeration system, the sulfur dioxide gas emitted by the burning sulfur stick will react with moisture in the air to produce a visible white smoke or fog. This smoke serves as a visual indicator of the location of the leak, allowing operators or technicians to identify and locate the source of the leak.
4. Safety Precautions: It's important to note that sulfur dioxide gas can be hazardous in high concentrations, causing irritation to the respiratory system and other health effects. Therefore, sulfur sticks should be used with caution in well-ventilated areas, and appropriate safety measures should be taken to minimize exposure to the gas.

Overall, sulfur sticks provide a simple and effective method for detecting leaks in enclosed spaces by producing visible smoke in response to the presence of sulfur dioxide gas. They are commonly used in industrial settings, such as gas pipelines, refrigeration systems, and chemical processing facilities, to identify and repair leaks quickly and effectively.