combstion-flame

Which part of a candle flame is the hottest?

• Outer zone
• Middle zone
• Inner zone
• Dark zone

Which colour is observed in the outer zone of a candle flame?

• Blue
• Yellow
• Red
• Black

Why does the middle zone of a candle flame appear yellow?

• Due to complete combustion
• Due to glowing unburnt carbon particles
• Due to lack of fuel
• Due to presence of carbon dioxide

What happens when a matchstick is brought near the other end of a glass tube inserted in a candle flame?

• The flame is extinguished
• A new flame appears
• The glass tube melts
• The wax solidifies

Which of the following fuels has high calorific value?

• Wood
• Coal
• Petroleum
• All of the above

What is the unit of calorific value?

• Joules per kg
• Kilojoules per kg
• Newton per kg
• Watts per kg

What is released during the burning of carbon fuels like coal and petroleum?

• Oxygen
• Unburnt carbon particles
• Water vapour
• Hydrogen gas

Which gas is produced due to incomplete combustion of fuels?

• Carbon dioxide
• Carbon monoxide
• Nitrogen oxide
• Sulphur dioxide

Why is it dangerous to burn coal in a closed room?

• It produces carbon monoxide
• It increases oxygen concentration
• It creates high temperature
• It releases nitrogen gas

What does excessive carbon dioxide in the air cause?

• Acid rain
• Global warming
• Ozone depletion
• Air purification