Write True/False against the following statements and also correct the false statement.
(a) A physical process in which a substance reacts with oxygen to give off heat is called combustion.
(b) Water is the best extinguisher for fires involving electrical equipment.
(c) Alcohol, CNG and LPG are inflammable substances.
(d) Increased concentration of nitrogen in air is believed to cause global warming.
(e) Greater the calorific value, better is the fuel.
(f) Middle zone is the hottest zone of a flame.
(g) The substances which vaporise during burning, give flame.
(a) False
A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
(b) False
Carbon dioxide is the best extinguisher for fires involving electrical equipment.
(c) True
(d) False
Increased concentration of carbon dioxide in air is believed to cause global warming.
(e) True
(f) False
The outer zone is the hottest zone of a flame.
(g) True.
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- Fill in the blanks using the words given in the box. ignition, petrol, combustion, calorific value, combustible, inflammable(a) A chemical process in which a substance reacts with oxygen to give off heat is called ………………(b) Wood, paper, CNG are ……………substances.(c) The lowest temperature at which a substance catches fire is called its …………… temperature.(d) Ignition temperature of……………… is lower than that of wood.(e) The substances which have very low……………… temperature and can easily catch fire with a flame are called…………….. substances.(f) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its …………….
- Which zone of a candle flame is the hottest?
- Which is the best fire extinguisher for fires involving electrical equipment and inflammable materials like petrol?
- 1. Which is the hottest zone and the coolest zone of a flame ?2. Why does the middle zone of the candle flame glow with yellow colour ?
- In a candle flame, what is the colour of: (a) innermost zone (b) middle zone and (c) outer zone?
- (a) What is a flame? What type of substance, on burning, give a flame?(b) What is the difference between the burning of a candle and the burning of a fuel like coal.
- State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.(a) Cutting a log of wood into pieces is a chemical change. (True/ False)(b) Formation of manure from leaves is a physical change. (True/ False)(c) Iron pipes coated with zinc do not get rusted easily. (True/ False)(d) Iron and rust are the same substances. (True/ False)(e) Condensation of steam is not a chemical change. (True/ False)
- Why the flame of burning LPG gas is blue in colour, and the flame of a burning candle is orange and yellow?
- In which zone of a candle flame:(a) partial combustion of fuel takes places, and(b) complete combustion of fuel takes place?
- Tick True/False against the following statements.(a) Fossil fuels can be made in the laboratory.(b) CNG is more polluting fuel than petrol.(c) Coke is an almost pure form of carbon.(d) Coal tar is a mixture of various substances.(e) Kerosene is not a fossil fuel.
- A substance which reacts with oxygen giving heat is called a combustible substance. Which one of the following is a combustible substance?Iron nailGlassStone pieceWood
- For the following statements, write True (T) or False (F). If the statement is false, correct the statement.(a) \( -8 \) is to the right of \( -10 \) on a number line.(b) $– 100$ is to the right of $– 50$ on a number line.(c) Smallest negative integer is $– 1$.(d) $– 26$ is greater than $– 25$.
- Fill in the blanks with suitable words:(a) A fuel must be heated to its……… before it starts burning.(b) The most common supporter of combustion around us is……………..(c) Fire produced by burning oil cannot be controlled by…………………….(d) A liquid fuel used in homes is………(e) The amount of heat evolved when 1kg of a fuel is burnt completely is called its…………………..(f) The substance which vaporize during, give…………………..(g) Burning of wood and coal causes……………. of air.
- State whether the following statements are true or False. If false, give the correct statement.(a) The process of seeping of water into ground is called filtration.(b) 51% of the earth’s surface is covered with water.(c) Year 2003 was observed as the International Year of Freshwater.(d) Snow and ice both are solid forms of water.
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