Class 8 Science Chapter 6 MCQ

Matchstick does not burn by itself. A matchstick is lighted by rubbing it on the rough surface provided on the side of the matchbox. The heat produced by friction arises the temperature of the chemicals present on the matchstick head to their ignition temperature. Due to this, the chemicals present on the head of the matchstick catch fire and the matchstick starts burning.

Here, all the statements are correct. Hence, your answer will be option [D].

A good fuel does not produce any harmful gases or leaves and any residue after burning. So, incorrect statement is option [C].

Here, all the statements are correct. Hence, your answer will be option [D].

Hydrogen gas is considered as cleanest fuel. Unlike carbon-based fuels, hydrogen produces no harmful by-products on combustion. Only energy and clean water are produced.

Here, all the statements are correct. Hence, your answer will be option [D].

In villages, people use wood as fuel because of its easy availability and low cost.

Calorific value of coal is higher than that of wood. Rest of all are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Forest fires are not due to cutting of trees.

The heat and light produced in the sun are not due to ordinary combustion which takes place in the presence of oxygen of air. In the sun, heat and light are produced due to nuclear reactions in which “hydrogen is converted into helium” with the release of heat and light.

Those substances which can undergo combustion are called combustible substances.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

It is very easy to burn a heap of dry leaves. We know that it is difficult to burn a heap of green leaves. The green leaves contain a lot of water. This water does not allow the green leaves to get heated to their ignition temperature easily and makes the burning of green leaves difficult. On the other hand, dry leaves do not contain water, they get heated to their ignition temperature easily and hence can catch fire easily.

Any fire needs three things to represent will, combustible substance, air (or oxygen) and heat. If any one of these three things is removed, then the burning will stop and fire will be extinguished.

The flame extinguishes because of non-availability of oxygen. Air or oxygen is necessary for combustion.

The spontaneous combustion which take place in nature are very dangerous.

Charcoal is a solid fuel which does not vaporize on heating. So, charcoal does not burn by producing a flame. It only glows on combustion.

The calorific value of LPG is much higher than the calorific value of coal. The calorific value of LPG is much higher than the calorific value of cow dung cakes or coal. This means that the burning of a given amount of LPG will produce much more heat than burning the same amount of cow dung cakes or coal.

It has a high calorific value. Hence, it produces a large amount of heat.

Those substances which do not burn are called non-combustible substance. Some of the non-combustible substances are stone, glass, cement, soil and iron nails etc.

LPG has the highest calorific value i.e. 55,000 kJ/kg. It means that if 1 kg of LPG is burnt completely, then it will produce 55,000 kilojoules of heat energy. Note: Fuel Calorific value Kerosene 45000 kJ/kg Biogas 35000 – 40000 kJ/kg Petrol 45000 kJ/kg.

Wood is a combustible substance. It is a solid fuel and produces smoke during combustion.

Here, all the statements are correct. Hence, your answer will be option [D].