Class 8 Science

Combustion

Extra Questions

Question 1: Which of these is a combustible substance?

  1. Asbestos
  2. Paper
  3. Stone
  4. Sand

Answer: (b) Paper

Question 2: Which of the following is non-combustible substance?

  1. Alcohol
  2. Coal
  3. Iron
  4. Wood

Answer: (c) Iron

Question 3: Which of the following is an inflammatory substance?

  1. Coal
  2. Alcohol
  3. Wood
  4. Stone

Answer: (b) Alcohol

Question 4: A flame has how many zones?

  1. One
  2. Two
  3. Three
  4. Four

Answer: (c) Three

Question 5: The outermost zone of flame is of which colour?

  1. Blue
  2. Orange
  3. Brown
  4. Dark

Answer: (a) Blue

Question 6: The middle zone of flame is of which colour?

  1. Blue
  2. Orange
  3. Transparent
  4. Black

Answer: (b) Orange

Question 7: Which is the best fuel for kitchen; in present times?

  1. LPG
  2. Coal
  3. Kerosne
  4. Petrol

Answer: (a) LPG

Question 8: Which part of flame is used by goldsmith?

  1. Blue
  2. Orange
  3. Black
  4. Green

Answer: (a) Blue

Question 9: Which of the following does not produce flame while burning?

  1. Wax
  2. Petrol
  3. Diesel
  4. Coal

Answer: (d) Coal

Very Short Answer Type Questions

Question 1: Define combustion?

Answer: Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Question 2: What is combustible substance?

Answer: A substance which can undergo combustion is called a combustible substance.

Question 3: What is a non-combustible substance?

Answer: A substance which cannot undergo combustion is called a non-combustible substance.

Question 4: What is ignition temperature?

Answer: Ignition temperature is the minimum temperature at which combustion starts in a substance.

Question 5: What is an inflammable substance?

Answer: A substance which has very low ignition temperature so that is can easily catch fire is called an inflammable substance, e.g. petrol, alcohol, etc.

Question 6: What is a fire extinguisher?

Answer: The substance which is used for putting off fire is called fire extinguisher.

Question 7: What is rapid combustion?

Answer: When combustion happens at a faster rate, it is called rapid combustion.

Question 8: Define calorific value of a fuel.

Answer: The amount of heat energy produced on combustion of 1 kg of a fuel is called calorific value of that fuel. It is expressed as kilo Joule per kg (kJ/kg).

Question 9: What is spontaneous combustion?

Answer: When combustion starts on its own; without an apparent cause; it is called spontaneous combustion.


Crop Production

The science of farming is called agriculture. Farming includes cultivation of plants and rearing of animals for food and other beneficial items.

Microorganisms: Friend or Foe

An organism which cannot be seen by naked eyes is called microorganism or microbe. We need a microscope to see a microbe.

Synthetic Fibres

ibres which are man-made are called synthetic fibres, e.g. nylon, acrylic, etc. A synthetic fibre is made of multiple units of a chemical substance.

Metals Non-metals

Metals are lustrous, sonorous, ductile, and are good conductor of heat and electricity.

Coal & Petroleum

Resources which from nature are called natural resources. Examples: coal, petroleum, air, water, soil, etc.

Combustion & Flame

Combustion is a chemical process in which a substance reacts with oxygen to give off heat. Some substances may also give light along with heat during combustion.

Conservation of Plants and Animals

The part of the earth where all living organisms are present is called biosphere. Biosphere is the narrow zone between hydrosphere, troposphere and atmosphere.

Cell: The Fundamental Unit of Life

The basic structural unit of a living organism is called cell. All living beings are made up of cells.

Reproduction in Animals

The process by which an organism produces its offspring is called reproduction. Reproduction is necessary to continue the lineage of an organism.

Reaching the Age of Adolescence

Adolescence is the period of life when many changes take place in the body, leading to reproductive maturity. Adolescence begins at around 10 years of age and lasts till 18 or 19 years of age.

Force & Pressure

A push or pull on an object is called force. Pressure is the force acting on a unit area on an object.

Friction

When one surface is moving over another surface, a force comes into play and opposes their relative motion. This force is called friction or force of friction.

Sound

Sound is a kind of wave which gives us the sense of hearing. Sound is produced by a vibrating body.

Chemical Effects of Electric Current

When electric current is passed through a conducing solution, some chemical reaction takes place in the solution. This is called chemical effect of electric current.

Natural Phenomena

Transfer of charge from one object to another is called charging. The process of transfer of charge to the earth is called earthing.

Light

When light falls on a shiny surface, most of it bounces back. This phenomenon is called reflection of light.

Solar System

The solar system is made up of the sun, its planets, satellites, asteroids, comets, dwarf planets, etc. All other members of the solar system keep on revolving around the sun.

Pollution

When air is contaminated with unwanted substances and becomes harmful for the living and non-living, this is called air pollution.