NCERT Class VIII Science Solutions: Chapter 6-Combustion and Flame Part 3

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VERY SHORT ANSWER QUESTIONS

Question 16:

Fill in the blanks in the following sentences.

  1. A ____________ process in which a substance reacts with __________ to give off heat is called combustion.

  2. When the clothes of a person catch __________, the person is covered with a __________ to extinguish fire.

  3. The __________ temperature at which a substance catches fire is called its __________ temperature.

  4. The substances which have very ________________ ignition temperature and can easily catch fire with a flame are called __________ substances.

  5. The substances which vapourises during __________, give flame.

Answer:

  1. A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

  2. When the clothes of a person catch fire, the person is covered with a blanket to extinguish fire.

  3. The lowest temperature at which a substance catches fire is called its ignition temperature.

  4. The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

  5. The substances which vapourises during burning, give flame.

Question 17:

Some words (underlined) in the following sentences are jumbled up. Write them in their correct form.

  1. Seldie is a combustible substance.

  2. Slags is a non-combustible material.

  3. Chittsmack does not burn by itself.

  4. Some substances on combustion produce thea and mafel.

  5. The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its ficalroic value.

Answer:

  1. Diesel is a combustible substance.

  2. Glass is a non-combustible material.

  3. Matchstick does not burn by itself.

  4. Some substances on combustion produce heat and flame.

  5. The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value.

Question 18:

Two glass jars A and B are filled with carbon dioxide and oxygen gases, respectively. In each jar a lighted candle is placed simultaneously. In which jar will the candle remain lighted for a longer time and why?

Answer:

In jar B, because oxygen is a supporter of combustion.

Question 19:

Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity.

Answer:

Anu should keep her test tube in the outermost zone which is the hottest part of the flame.

Question 20:

Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Gas (CNG) in big cities?

Answer:

It is because CNG produces harmful products in very small amount and is a cleaner fuel.