Combustion and Flame Quiz - CBSE Class 8 Science

Free practice quiz: Combustion and Flame (CBSE Class 8 Science). 20 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. Which of the following is NOT required for combustion to occur?

   1. Fuel
   2. Oxygen
   3. Heat
   4. Water
   Show answer

   Answer: D. Water

   Combustion requires fuel, oxygen, and heat. Water is a product of combustion, not a requirement.

2. Why does a matchstick burn more rapidly when blown?

   1. Increased oxygen supply
   2. Increased heat
   3. Decreased oxygen supply
   4. Decreased heat
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   Answer: A. Increased oxygen supply

   Blowing on a matchstick increases the supply of oxygen, which helps to accelerate the combustion process.

3. Describe the conditions necessary for spontaneous combustion.

   1. Low temperature and high oxygen
   2. High temperature and low oxygen
   3. High temperature and sufficient oxygen
   4. Low temperature and sufficient oxygen
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   Answer: C. High temperature and sufficient oxygen

   Spontaneous combustion occurs when a substance ignites without any external ignition source due to slow oxidation which gradually generates heat. Sufficient oxygen is needed for this oxidation and a build-up of heat.

4. Analyze the effect of different factors (e.g., surface area, concentration of oxygen) on the rate of combustion.

   1. No impact on rate
   2. Factors have no predictable effect
   3. Increased surface area and oxygen concentration increase the rate
   4. Increased surface area decreases the rate, more oxygen increases the rate
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   Answer: C. Increased surface area and oxygen concentration increase the rate

   Increased surface area provides more contact with oxygen, increasing the rate of combustion. Higher oxygen concentration provides more reactant, also increasing the combustion rate.

5. Explain the chemical reactions involved in the different zones of a candle flame.

   1. Only one reaction happens
   2. All zones have identical reactions
   3. Reactions differ due to varying oxygen availability and temperatures in different zones
   4. No chemical reactions occur
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   Answer: C. Reactions differ due to varying oxygen availability and temperatures in different zones

   The innermost zone has incomplete combustion, the middle zone shows luminous flame due to incomplete combustion of wax vapors while the outermost zone has complete combustion.

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