NCERT Solutions for Chapter: Combustion and Flame, Exercise 4: LONG ANSWER QUESTIONS

 You are provided with three watch glasses containing milk, petrol and mustard oil, respectively. Suppose you bring a burning candle near these materials one by one, which material(s) will catch fire instantly and why?

Manu was heating oil to fry potato chips. The cooking oil all of a sudden caught fire; he poured water to extinguish the fire. Do you think this action was suitable. If yes, why? If not, why not? In such a condition what should Manu have done?

 What are the three essential requirements to produce fire? How fire extinguisher is useful for controlling the fire.

Give two examples each for a solid, liquid and gaseous fuel along with some important uses.

 The calorific values of petrol and CNG are$45000 \mathrm{kJ}/\mathrm{kg} \mathrm{and} 50,000 \mathrm{kJ}/\mathrm{kg}$, respectively. If you have vehicle which can run on petrol as well as CNG, which fuel will you prefer and why?

 Although wood has a very high calorific value, we still discourage its use as a fuel. Explain.

Forest fire produces a lot of air pollution. Write in brief about the reasons of forest fires.

 Complete the crossword with the help of the clues:

Across

1. Non-metal which catches fire if exposed to air $\left(10\right)$

3. The lowest temperature at which a substance catches fire is called its _____ temperature. $\left(8\right)$

5. The most common fire extinguisher. $\left(5\right)$

Down

 2. A chemical process in which a substance reacts with oxygen to give off heat. $\left(10\right)$

 4. Petrol is used as a _____ in automobiles. $\left(4\right)$

 6. It is as hard as stone and black in colour. $\left(4\right)$