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Q1. The process of burning a substance in the presence of air or oxygen to release heat and light is called:
Combustion is a chemical reaction in which a substance reacts with oxygen to release energy in the form of heat and light. Evaporation is a physical process of liquid changing to gas, condensation is gas to liquid, and respiration is a biochemical process in living organisms. Combustion is the correct term for burning.
Q2. The lowest temperature at which a substance catches fire and starts burning is known as its:
Ignition temperature is the lowest temperature at which a substance catches fire and starts burning. Boiling point is the temperature at which a liquid boils, melting point is the temperature at which a solid melts, and freezing point is the temperature at which a liquid freezes. Ignition temperature is specific to combustion.
Q3. Which of the following is a combustible substance?
Wood is a combustible substance because it can catch fire and burn when exposed to a flame. Stone, iron nail, and water are non-combustible substances—they do not burn. Combustible substances are those that undergo combustion in the presence of air and heat.
Q4. Which of the following is a non-combustible substance?
Glass is a non-combustible substance because it does not burn when exposed to fire. Paper, cloth, and kerosene are combustible substances. Non-combustible substances do not catch fire or support combustion.
Q5. The head of a matchstick contains a mixture of:
The head of a matchstick contains a mixture of antimony trisulphide and potassium chlorate. These chemicals react when heated by friction to produce fire. Sand, iron, sulfur, chalk, and carbon are not the correct components.
Q6. The rubbing surface on a matchbox contains:
The rubbing surface on a matchbox contains glass powder and red phosphorus. Glass powder provides friction, and red phosphorus helps in ignition. Wax, wood, water, oxygen, sand, and sugar are not the correct materials.
Q7. The substance that helps a fire to burn by supplying oxygen is called a:
A supporter of combustion is a substance that helps fire burn by supplying oxygen. Oxygen is the most common supporter of combustion. Fuel is the substance that burns, igniter provides the heat, and inhibitor stops combustion.
Q8. Which of the following is an example of rapid combustion?
Burning of LPG in a stove is an example of rapid combustion because it burns quickly with a flame. Rusting of iron is slow combustion, digestion of food is a biochemical process, and formation of coal takes millions of years (not combustion).
Q9. The type of combustion in which a substance suddenly bursts into flames without any apparent cause is called:
Spontaneous combustion is the type of combustion in which a substance suddenly bursts into flames without any apparent cause, due to self-heating. Rapid combustion requires external heat, slow combustion occurs over time, and explosion is a sudden release of energy.
Q10. A large amount of gas, heat, light, and sound is produced suddenly in a process known as:
An explosion is a process in which a large amount of gas, heat, light, and sound is produced suddenly. It occurs when combustion happens very rapidly. Rapid combustion is fast but not necessarily explosive, slow combustion is gradual, and spontaneous combustion occurs without external ignition.
Q11. Which of the following is an essential condition for combustion?
The three essential conditions for combustion are: (1) fuel, (2) oxygen (or supporter of combustion), and (3) heat (to reach the ignition temperature). All three are necessary for fire to occur. Without any one of them, combustion cannot take place.
Q12. Water is often used to control fires because it:
Water extinguishes fire by two methods: it cools the burning material below its ignition temperature, and it forms a layer that cuts off the oxygen supply. Water does not act as a fuel, increase oxygen, or raise ignition temperature.
Q13. Which type of fire should never be extinguished with water?
Electrical and oil fires should never be extinguished with water. Water conducts electricity and can cause electric shock in electrical fires. Oil fires spread because oil floats on water. Wood, paper, and cloth fires can be extinguished with water.
Q14. The fire extinguisher that is most suitable for an electrical fire is:
Sand or carbon dioxide extinguishers are suitable for electrical fires because they do not conduct electricity and cut off the oxygen supply. Water should not be used for electrical fires. Wooden logs and cloth are not extinguishing agents.
Q15. In a candle flame, the zone of complete combustion is the:
The outermost zone of a candle flame is the zone of complete combustion. It is blue in color, has the highest temperature, and is non-luminous. The middle zone has incomplete combustion, and the innermost zone contains unburnt wax vapors.
Q16. The middle zone of a candle flame is yellow and luminous because:
The middle zone of a candle flame is yellow and luminous because of the presence of unburnt carbon particles that get heated and glow. This zone has incomplete combustion. It is not the coolest part, nor does it contain water vapor.
Q17. The innermost part of a candle flame is:
The innermost part of a candle flame is a dark zone containing unburnt wax vapors. It is the coolest part of the flame and does not have enough oxygen for combustion. It is not the hottest zone or the zone of complete combustion.
Q18. The maximum temperature in a candle flame is found in the:
The outermost zone of a candle flame has the maximum temperature because it is the zone of complete combustion. The middle zone has lower temperature, and the innermost zone is the coolest. The wick itself is not the hottest part.
Q19. Water can be heated in a paper cup without the cup burning because:
When water is heated in a paper cup, the water absorbs the heat, keeping the temperature of the paper below its ignition temperature. Paper is combustible, but the heat is transferred to the water. Water does not act as a fuel; it absorbs heat.
Q20. The substance that does not burn in air but supports the process of burning is:
Oxygen does not burn itself but supports the process of burning. It is essential for combustion. Hydrogen is combustible, carbon dioxide and nitrogen are non-combustible and do not support burning.
Q21. Which of the following fuels has the lowest ignition temperature?
Paper has a low ignition temperature and catches fire easily. Wood and coal have higher ignition temperatures, and iron is non-combustible. Paper ignites at a lower temperature than wood and coal.
Q22. To control a fire caused by burning kerosene, it is best to:
Kerosene fires should not be extinguished with water because kerosene floats and spreads. Sand or a fire extinguisher cuts off the oxygen supply. Fanning flames would worsen the fire, and adding more kerosene is dangerous.
Q23. Which of the following is a liquid fuel commonly used for cooking in many homes in Jammu and Kashmir?
Kerosene and LPG are commonly used liquid and gaseous fuels for cooking in Jammu and Kashmir. Wood and cow dung cakes are solid fuels used in rural areas, but kerosene and LPG are more widely used in urban homes.
Q24. The process of slow combustion occurs in:
Rusting of iron is an example of slow combustion because it occurs slowly over time without a flame. Burning of a candle and LPG are rapid combustion, and bursting of a cracker is an explosion. Slow combustion releases energy gradually.
Q25. Which of the following is not an example of combustion?
Digestion of food is a biochemical process, not combustion. Burning of wood, coal, and incense sticks are all examples of combustion where substances react with oxygen to release heat and light.
Q26. The chemical name of LPG is:
LPG stands for Liquefied Petroleum Gas. It is a mixture of propane and butane gases stored in liquid form under pressure. It is a clean-burning fuel used for cooking and heating.
Q27. The minimum amount of air or oxygen needed for combustion is called the:
The minimum amount of air or oxygen needed for combustion is called the critical point. Below this amount, combustion cannot occur. Ignition point is the temperature, and combustion point and supporter level are not standard terms.
Q28. In which zone of a candle flame does incomplete combustion take place?
Incomplete combustion takes place in the middle zone of a candle flame, where there is not enough oxygen for complete burning. This zone is yellow and luminous due to glowing carbon particles. The innermost zone has no combustion, and the outermost zone has complete combustion.
Q29. The color of the outermost zone of a candle flame is usually:
The outermost zone of a candle flame is blue in color. It is the zone of complete combustion and has the highest temperature. The middle zone is yellow, and the innermost zone is dark. Blue indicates complete burning.
Q30. A substance which readily catches fire and burns rapidly is called:
Inflammable substances are those that readily catch fire and burn rapidly. Petrol, alcohol, and LPG are examples. Non-combustible substances do not burn, fireproof materials resist burning, and slow-burning substances burn slowly.
Q31. In a fire caused by an electrical short circuit, the first step should be to:
In an electrical fire, the first step is to switch off the main power supply to prevent electric shock and further damage. Water should never be used on electrical fires. Calling the fire brigade is important but not the first step.
Q32. The head of a matchstick catches fire when struck against the rubbing surface because:
When a matchstick is struck against the rubbing surface, friction produces heat. This heat ignites the chemicals on the match head, causing it to catch fire. The matchstick is not wet, made of glass, or ignited by oxygen in the rubbing surface.
Q33. Which of the following is a gaseous fuel?
Natural gas is a gaseous fuel used for heating and cooking. Petrol, kerosene, and diesel are liquid fuels. Natural gas is cleaner and more efficient than many other fuels.
Q34. The substance that does not support combustion is:
Carbon dioxide does not support combustion. It is used in fire extinguishers to put out fires by cutting off the oxygen supply. Oxygen and air support combustion, and ozone is a form of oxygen.
Q35. A matchstick does not catch fire on its own at room temperature because:
A matchstick does not catch fire at room temperature because its ignition temperature is higher than room temperature. It needs heat from friction to reach its ignition point. It is combustible and has oxygen available, but it is not wet.
Q36. In the absence of one of the three essential conditions for combustion, fire:
Fire requires fuel, oxygen, and heat (ignition temperature). If any one of these is missing, the fire gets extinguished. This is the principle behind firefighting methods.
Q37. Which of the following is a combustible substance used as fuel in rural areas of Jammu and Kashmir?
In rural areas of Jammu and Kashmir, dried wood and dung cakes are commonly used as fuel for cooking and heating. Plastic, metal sheets, and clay are not used as fuels. These traditional fuels are combustible.
Q38. The principle behind using sand to extinguish a fire is:
Sand extinguishes fire by cutting off the oxygen supply. When sand is thrown over burning material, it forms a layer that prevents oxygen from reaching the fuel, thus extinguishing the fire. It does not increase oxygen, temperature, or add fuel.
Q39. A substance that has a very low ignition temperature and can easily catch fire is called:
Inflammable substances have a very low ignition temperature and catch fire easily. Examples include petrol, alcohol, and LPG. Non-combustible substances do not burn, fireproof materials resist burning, and slow-burning substances burn slowly.
Q40. Which of the following statements is true about the ignition temperature of a fuel?
Ignition temperature is the minimum temperature at which a fuel starts burning. It varies for different fuels. It is not the same for all fuels, not the boiling point, and is not lower for coal than for paper (paper has a lower ignition temperature than coal).
Q41. In a candle flame, the unburnt wax vapors are found in the:
The innermost zone of a candle flame contains unburnt wax vapors. It is the coolest part of the flame and lacks sufficient oxygen for combustion. The middle zone has incomplete combustion, and the outermost zone has complete combustion.
Q42. Why is LPG considered a better domestic fuel than wood?
LPG is a better domestic fuel than wood because it has a higher calorific value (more heat per unit mass) and burns without smoke. It is not cheaper in all cases, is not a solid fuel, and has a lower ignition temperature compared to wood.
Q43. Which of the following is an example of a non-combustible substance?
Asbestos is a non-combustible substance used as a fireproof material. Petrol, straw, and diesel are combustible substances that catch fire easily. Non-combustible substances do not burn.
Q44. The process of burning of a magnesium ribbon in air is an example of:
Burning of a magnesium ribbon in air is an example of rapid combustion. It burns with a dazzling white flame and releases a large amount of heat and light quickly. It is not slow, spontaneous, or an explosion.
Q45. Water should not be used to extinguish a fire caused by petrol because:
Petrol is lighter than water, so it floats on top and the fire spreads. This is why water should not be used on petrol fires. Instead, sand or a fire extinguisher should be used. Petrol is not soluble in water, not heavier, and water does not increase ignition temperature.
Q46. The colorless, odorless gas that is essential for combustion is:
Oxygen is the colorless, odorless gas essential for combustion. It supports burning and is a key component of air. Carbon dioxide does not support combustion, nitrogen is neutral, and hydrogen is combustible but not the supporter.
Q47. A student performs an experiment by placing a glass chimney over a burning candle. The candle extinguishes after some time because:
When a glass chimney is placed over a burning candle, the oxygen inside the chimney is gradually used up. Once the oxygen is depleted, the candle extinguishes. This shows that oxygen is essential for combustion.
Q48. Which of the following is a safety measure to prevent fire accidents at home?
Keeping LPG cylinders in a well-ventilated area is a safety measure to prevent fire accidents. Inflammable substances should be kept away from stoves, water near electrical appliances is dangerous, and using multiple plugs in one socket can cause short circuits.
Q49. The type of combustion that occurs in a coal mine due to the presence of coal dust and air is:
In coal mines, coal dust and air can cause spontaneous combustion. The heat generated by slow oxidation builds up and ignites the coal without an external flame. This is a serious hazard in mines.
Q50. When water is poured over a burning wood fire, it extinguishes because:
Water extinguishes a wood fire by two methods: it cools the burning wood below its ignition temperature, and it cuts off the oxygen supply by forming steam. Wood does not dissolve in water, and water does not supply oxygen or increase ignition temperature.