Question

A substance which reacts with oxygen giving heat is called a combustible substance. Which one of the following is a combustible substance?

• A. Iron nail
• B. Glass
• C. Stone piece
• D. Wood

Answer 1

The correct option is D

Wood

Explanation for the correct option:

Option D: Wood

1. Combustible substances are those that burn or undergo combustion easily and catch fire.
2. Combustion is a chemical reaction in which a material combines with oxygen to produce light and heat.
3. They need to be carefully handled as they can catch fire easily.
4. These substances have low ignition temperature i.e. the lowest temperature at which when they are heated and can catch fire.
5. Examples: Wood, coal, petrol, diesel, charcoal, etc.
6. Due to its great tendency to catch fire and burn when exposed to heat, wood releases chemicals that react rapidly with oxygen.

Explanation for the incorrect options:

Option A: Iron nail

1. A substance that does not ignite, burn, or sustain combustion is said to be non-combustible. When heated or exposed to fire, it does not release combustible fumes.
2. Because of the strong intermolecular force of attraction, iron is not a flammable substance.
3. Hence, it is an incorrect option.

Option B: Glass

1. Glass is mainly comprised of oxides like silica.
2. The greatest oxidation states of these elements prevent them from reacting with oxygen. Glass is therefore not flammable.
3. Hence, it is an incorrect option.

Option C: Stone piece

1. A stone piece is made up of tiny rock and clay fragments. Therefore, it lacks organic material that would burn in the presence of air, that's why is not flammable.
2. Hence, it is an incorrect option.

Hence, Wood is a combustible substance.