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Question
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) Increase concentration of nitrogen in the air is believed to cause global warming.
(e) Greater the calorific value, the better the fuel.
(f) Middle zone is the hottest zone of a flame.
(g) The substances which vapourize during burning, give flame.
(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) Increase concentration of nitrogen in the air is believed to cause global warming.
(e) Greater the calorific value, the better the fuel.
(f) Middle zone is the hottest zone of a flame.
(g) The substances which vapourize during burning, give flame.
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Solution
(a) Combustion is a chemical process. Therefore, the given statement is false. It can be corrected as,
A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
A substance that undergoes combustion is said to be combustible. It is also
called a fuel.
(b) Water conducts electricity, so water should never be used in a situation with electrical appliances. If it is used, it will harm those who are trying to put off the fire . Hence, the given statement is false. It can be corrected as,
Carbon dioxide is the best extinguisher for fires involving electrical equipment.
(c) The substances which have very low ignition temperature and can easily catch fire are called inflammable substances. Such substances include petrol, alcohol, Liquified Petroleum Gas (LPG), CNG, etc. Therefore, the given statement is true.
(d) Global warming is the rise in temperature of the atmosphere of the Earth. Combustion of fuels releases carbon dioxide in the environment. This carbon dioxide level increase in the air can cause global warming. Hence, the given statement is false. It can be corrected as,
Increased concentration of carbon dioxide in the air is believed to cause global warming.
(e) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. Calorific value is directly proportional to its efficiency. That is, if the calorific value of a fuel is high, its efficiency will also be high. Hence, the given statement is true.
(f) A Flame consist of three zones namely outer zone, middle zone and inner zone. Outer zone is the hottest zone, middle zone is the moderately hot zone and inner zone is the least hot zone. Hence, the given statement is false. It can be corrected as,
Outer zone is the hottest zone of a flame.
(g) The substances which evaporate during burning, give flames. For example, molten wax rise through the wick and is vapourized during burning and hence form flames. Therefore, the given statement is true.
A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
A substance that undergoes combustion is said to be combustible. It is also
called a fuel.
(b) Water conducts electricity, so water should never be used in a situation with electrical appliances. If it is used, it will harm those who are trying to put off the fire . Hence, the given statement is false. It can be corrected as,
Carbon dioxide is the best extinguisher for fires involving electrical equipment.
(c) The substances which have very low ignition temperature and can easily catch fire are called inflammable substances. Such substances include petrol, alcohol, Liquified Petroleum Gas (LPG), CNG, etc. Therefore, the given statement is true.
(d) Global warming is the rise in temperature of the atmosphere of the Earth. Combustion of fuels releases carbon dioxide in the environment. This carbon dioxide level increase in the air can cause global warming. Hence, the given statement is false. It can be corrected as,
Increased concentration of carbon dioxide in the air is believed to cause global warming.
(e) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. Calorific value is directly proportional to its efficiency. That is, if the calorific value of a fuel is high, its efficiency will also be high. Hence, the given statement is true.
(f) A Flame consist of three zones namely outer zone, middle zone and inner zone. Outer zone is the hottest zone, middle zone is the moderately hot zone and inner zone is the least hot zone. Hence, the given statement is false. It can be corrected as,
Outer zone is the hottest zone of a flame.
(g) The substances which evaporate during burning, give flames. For example, molten wax rise through the wick and is vapourized during burning and hence form flames. Therefore, the given statement is true.
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