F.
Short Answer Questions
1. What is combustion, and what are the essential requirements for combustion?
Ans-
Combustion is a chemical process in which a substance reacts rapidly with
oxygen to produce heat and light.
Essential requirements: (i) Fuel, (ii) Oxygen (air), (iii) Ignition temperature.
2. Explain the concept of ignition temperature and provide an example.
Ans-
The ignition temperature is the minimum temperature at which a substance
catches fire.
Example: Paper ignites at a lower temperature than wood.
3. How is fire typically controlled, and what are the three essential requirements
for fire to burn?
Ans-
Fire is controlled by removing heat, cutting off oxygen, or removing fuel.
Three requirements: fuel, oxygen, and ignition temperature.
4. What is the purpose of a fire extinguisher, and how do they work?
Ans-
A fire extinguisher puts out fire by cutting the oxygen supply or lowering the
temperature below ignition point.
5. Define spontaneous combustion and provide an example.
Ans-
Spontaneous combustion is burning of a substance without external heating, due
to internal heat buildup.
Example: Burning of coal heaps or oily rags.
6. What is the significance of the colour of a flame, and how does it relate to the
materials being burned?
Ans-
The flame’s colour indicates burning efficiency and the material. Blue flame =
complete combustion (e.g., LPG); Yellow flame = incomplete combustion (e.g.,
candle).
G. Detailed Answer Questions
1. Describe the different types of fuels mentioned in the text and their uses in
daily life.
Ans-
Fuels are substances that produce energy on burning.
Solid fuels: Wood, coal, charcoal – used in cooking, heating, and industries.
Liquid fuels: Kerosene, petrol, diesel – used in vehicles, lamps, and machines.
Gaseous fuels: CNG, LPG, biogas – used in cooking, transport, and eco-friendly
energy supply.
2. Explain how the colour of a flame provides information about the materials
burning and give examples.
Ans-
Flame colour depends on the type of combustion:
Blue flame → complete combustion, efficient fuel use (e.g., LPG stove).
Yellow flame → incomplete combustion, soot formation (e.g., candle, kerosene
lamp).
Red/Orange flame → lower temperature burning.
This helps identify combustion efficiency and pollution.
3. Discuss the calorific value of fuels and its importance in fuel selection. Which
fuel would you choose to boil water, considering calorific values?
Ans-
Calorific value is the amount of heat produced by burning 1 kg of fuel. Higher
calorific value = more energy, less wastage.
Examples:
Wood ≈ 17,000 kJ/kg
Coal ≈ 25,000–33,000 kJ/kg
LPG ≈ 55,000 kJ/kg
To boil water quickly and efficiently, LPG is the best choice.
4. What are the environmental consequences of using traditional carbon-based
fuels like wood and coal? How does the use of cleaner fuels like CNG help
mitigate these issues?
Ans-
Consequences of wood/coal: Air pollution, smoke, greenhouse gases (CO₂), acid
rain, deforestation.
Cleaner fuels (CNG, LPG): Produce less smoke, no harmful residues, reduce air
pollution, safer for health and environment.
5. Can you describe the mechanism by which a matchstick ignites and explain the
role of white phosphorus and red phosphorus in modern safety matches?
Ans-
A matchstick head contains potassium chlorate, sulfur, and glue.
Earlier matches used white phosphorus (toxic, dangerous).
Modern safety matches use red phosphorus on the side strip.
When struck, red phosphorus converts to white phosphorus, which ignites at low
temperature, lighting the match safely.
6. How does conductivity relate to the ignition of substances? Provide examples
of inflammable substances.
Ans-
Good conductors like metals absorb heat quickly but don’t catch fire easily. Poor
conductors like wood or paper heat up faster and ignite.
Inflammable substances: Petrol, alcohol, LPG, kerosene – they catch fire easily at
low ignition temperatures.
