Test: Combustion and Flame- 1 (UPSC Level) - UPSC MCQ

1. The first statement is correct. Explosive combustion is characterized by a very rapid reaction that releases a large amount of gas, along with heat, light, and sound. This definition aligns with the characteristics of explosions, such as those seen in firecrackers and dynamite.

2. The second statement is also correct. The outermost part of the flame is indeed the hottest part due to complete combustion, which occurs here with an adequate supply of oxygen. This results in a blue color, indicating the high temperature and complete burning of the fuel.

3. The third statement is incorrect. Charcoal does not produce a flame because it does not vaporize upon combustion; it undergoes direct combustion without turning into a gaseous form, which is why it doesn't produce a flame.

Thus, only statements 1 and 2 are correct, making Option B the correct answer.

Both Statement-I and Statement-II are factually correct. Statement-I correctly defines fuel efficiency as the calorific value of a fuel, measured in kilojoules per kg. Statement-II accurately highlights the danger of burning coal in enclosed spaces due to the risk of carbon monoxide accumulation. However, it is important to note that these two statements address different aspects of fuel combustion and safety, without one directly explaining the other. Statement-I focuses on fuel efficiency measurement, while Statement-II emphasizes the dangers associated with burning coal in confined areas. Therefore, the correct answer is option (b), as both statements are correct but do not have a direct explanatory relationship.

In the context of the statements provided, Statement-I explains the general use of water to control fire effectively by lowering the temperature of the combustible material and cutting off the air supply to extinguish the fire. Statement-II provides a specific scenario where water may not be effective in controlling fire, such as in the case of oil or petrol fires due to their properties. Both statements are factually correct but are addressing different aspects of fire control. Statement-II does not explain Statement-I but rather adds additional information regarding specific cases where water may not be effective in extinguishing a fire. Hence, the correct choice is Option B.

1. Phosphorus - Ignites at 35°C: Correct. Phosphorus does indeed ignite at a temperature as low as 35°C, making it a substance with a relatively low ignition temperature.

2. Kerosene - Requires high temperature to ignite: Incorrect. Kerosene is known for having a relatively low ignition temperature. It can ignite with a slight increase in temperature, unlike substances such as wood, which require much higher ignition temperatures.

3. Matchstick - Burns without needing ignition temperature: Incorrect. A matchstick requires reaching its specific ignition temperature to burn. It does not ignite spontaneously without reaching this temperature.

4. Inflammable Substances (e.g., Diesel) - Low ignition temperature: Correct. Inflammable substances, such as diesel, are characterized by their low ignition temperatures, which allow them to catch fire easily.

Based on the analysis, pairs 1 and 4 are correctly matched.

Statement I highlights the composition and functioning of early safety matches, emphasizing the hazardous nature of white phosphorus. Statement II contrasts this with modern safety matches, explaining the components and the safer process of ignition involving red phosphorus converting to white phosphorus. Both statements are accurate, and Statement II elaborates on the advancements in safety measures in match production, making Option A the correct choice.

1. Antimony Trisulphide - Provides frictional heat: Incorrect. Antimony trisulphide is used as a combustible material in the match head, not for providing frictional heat. Frictional heat is generated by the striking surface, which contains powdered glass.
2. Potassium Chlorate - Acts as an oxidizing agent: Correct. Potassium chlorate is an oxidizing agent that helps in the combustion process by providing oxygen.
3. White Phosphorus - Used in modern safety matches: Incorrect. White phosphorus is not used in modern safety matches due to its hazardous nature. Modern matches use red phosphorus, which is safer.
4. Red Phosphorus - Present on the striking surface: Correct. Red phosphorus is present on the striking surface of safety matches. When the match is struck, red phosphorus is converted to white phosphorus, which then reacts with potassium chlorate to ignite the match.
Thus, pairs 2 and 4 are correctly matched.

Water is not suitable for extinguishing fires involving electrical equipment or oil because it is a good conductor of electricity. Using water in such cases can lead to disastrous consequences as it may conduct electricity and pose a risk to individuals attempting to control the fire. Therefore, it is crucial to avoid using water to extinguish fires involving electrical equipment or oil to prevent harm and further damage.

1. Coal - Liquid Fuel: Incorrect. Coal is a solid fuel, not a liquid fuel. Solid fuels are materials that are in a solid state and combust to produce energy. Coal is one of the most commonly used solid fuels.

2. Charcoal - Solid Fuel: Correct. Charcoal is indeed a solid fuel. It is created by heating wood or other organic substances in the absence of oxygen and is widely used for cooking and heating purposes.

3. Methane - Fuel Gas: Correct. Methane is a fuel gas. It is a simple hydrocarbon and is used extensively as a fuel due to its high energy content and clean-burning properties.

4. Crude Oil - Solid Fuel: Incorrect. Crude oil is a liquid fuel. It is a naturally occurring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials. It is processed into various products like gasoline, diesel, and other petrochemicals.

Thus, two pairs are correctly matched: Charcoal - Solid Fuel and Methane - Fuel Gas.

Statement-I defines combustion accurately, while Statement-II explains non-combustible substances. Although both statements are correct individually, they are not directly related or explanatory of each other. Statement-I talks about combustion, while Statement-II discusses non-combustible substances, which are distinct concepts. Therefore, option B is the correct choice as both statements are correct but not interrelated in terms of explanation.

The correct answer is Option C: Ignition temperature. Ignition temperature, also known as the ignition point, is the minimum temperature at which a substance can start to burn and combust. This temperature varies for different substances and is crucial for initiating the combustion process. Without reaching this specific temperature, a substance will not catch fire even if exposed to a flame. It's a critical concept in understanding the conditions required for combustion to occur effectively.