Ncert – class 8- science – Chapter 4: Combustion and Flame 1 Welcome to your Ncert - class 8- science - Chapter 4: Combustion and Flame 1 1. A thin paper cup filled with water does not catch fire when placed over a flame. This is because: the water cuts off oxygen supply to the paper cup water is an excellent conductor of heat the paper cup does not reach to ignition temperature paper is a poor conductor of heat None 2. Explosion of crackers takes place due to application of _________ on them. pressure heat temperature none of these None 3. I. The most significant way in which humans are exposed to mercury is through drinking water.��II. A great deal of mercury enters the atmosphere because of coal-burning power plants. Statement I is true, Statement II is true Statement I is true, Statement II is false Statement I is false, Statement II is true Statement I is true, Statement II is true and is a correct explanation of the phenomena described in I None 4. How carbon dioxide is stored in the house to extinguish fire? It can store in the cylinders under high pressure It can store in canes It can store in the bottles It can not store in any form None 5. What reactant must be present for a reaction to be classified as combustion? O2 Cl4 CH4 CO None 6. Which chemical substance is emitted in car exhaust and is a cause of acid rain? Carbon dioxide Nitrogen oxides DDT Lead None 7. A white solid X reacts with dil.HCl to give colourless gas which is used in fire extinguishers. The solid X is: NaHCO3 $$Na_{2}Co_{3}$$ NaCl $$CH_{3}COONa$$ None 8. Which of the following happen when a wax candle is burnt(i) Fuel undergo oxidation(ii)Liberation of heat and light energy (iii) release of water vapour and carbondioxide (i), (ii) and (iii) (i) and (ii) only (ii) and (iii) only (iii) and (i) only None 9. The cooking gas burns rapidly and produces heat and light. Such combustion is called _________. incomplete combustion none of these rapid combustion regular combustion None 10. The heat liberated per kilogram of a fuel is called its: calorific value fuel value weight value mass value None 11. When fuel is added to the exhaust (burnt) gases in a jet engine combustion takes place. Some facts are mentioned here about this combustion. Pick the false one? It increases the intake of oxygen from the air It is known as 'after burning' It reduces fuel consumption It gives additional thrust None 12. Which of the following example represents spontaneous combustion? Ignition of a cracker. Phosphorus burns in air at room temperature Burning of matchstick. Burning of cooking gas. None 13. Fire extinguishers containing CO2 are the best extinguishers for fires involving electrical equipment: None of these because CO 2 being heavier than oxygen covers the fire like a blanket. because CO2 being lighter than oxygen covers the fire like a blanket. because CO2 being heavier than oxygen increases fire. None 14. How water helps in extinguishing fire? Water cools the combustible material so that its temperature is brought above the ignition temperature. Water cools the combustible material so that its temperature is brought below the ignition temperature. Water heats the combustible material so that its temperature is brought below the ignition temperature. None of these None 15. Which of the following are the characteristics of Indian coal?1. High ash content2. Low sulphur content3. High sulphur contentSelect the correct answer using the codes given. 1 and 3 only 2 only 1,2, and 3 1 and 2 only None 16. During burning of candle, different zones of combustion in the flame are listed below:-a) Outermost zoneb) Innermost zonec) Middle zone The correct order of temperature of zones is : B>C>A A>B>C C>B>A A>C>B None 17. For complete combustion of a fuel, it will need: an excess of air and high temperature an excess of air high air pressure high temperature None 18. If you watch a burning candle carefully, you will find different colurs in the flame. Which is the hottest part of the candle flame? The innermost black zone The outermost portion that is blue The middle orange part The middle, yellow part None 19. Which compound is formed due to incomplete combination of fuels? Carbon monoxide Oxygen Carbon dioxide Water None 20. Which of the following examples represents explosion? Burning of phosphorus in air at room temperature Ignition of a cracker Burning of cooking gas Burning of matchstick None Time's up Please Share This Share this content Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Leave a Reply Cancel replyCommentEnter your name or username to commentEnter your email address to commentEnter your website URL (optional) Save my name, email, and website in this browser for the next time I comment.
