Question 1

Which of the following is a combustible substance?

Accepted Answer

Wood is a combustible substance because it catches fire easily in the presence of oxygen and heat. Glass, stone, and iron nails are non-combustible materials as they do not catch fire.

Question 2

What is the essential requirement for combustion?

Accepted Answer

Air (oxygen) is essential for combustion. Without oxygen, a substance cannot burn. Water extinguishes fire, soil covers it, and carbon dioxide also suppresses it, but oxygen supports combustion.

Question 3

The lowest temperature at which a substance catches fire is called its:

Accepted Answer

Ignition temperature is defined as the lowest temperature at which a combustible substance catches fire. A substance cannot catch fire if its temperature is lower than its ignition temperature.

Question 4

Which substance has a very low ignition temperature and catches fire spontaneously at room temperature?

Accepted Answer

White phosphorus has a very low ignition temperature of about 35°C and catches fire spontaneously in air at room temperature. Therefore, it is stored under water.

Question 5

Which of the following is used to extinguish electrical fires?

Accepted Answer

Carbon dioxide ($CO2$) is the best extinguisher for fires involving electrical equipment and flammable materials like petrol because it is heavier than oxygen and covers the fire like a blanket.

Combustion and Flame