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It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.


The green leaves contain some water content with which the ignition temperature of leaves increases and they do not catch fire easily while dry leaves have no water so they catch fire easily.

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Explain how CO2 is able to control fires.


(i) CO2 forms a blanket around fire due to which supply of air (oxygen) is stopped.

(ii) CO2 also brings down the temperature of the fuel. 

Hence able to control fires.

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Name the unit in which the calorific value of a fuel is expressed.


 The calorific value of fuel is expressed in Kilojoules per kg (kJ/kg).

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Which zone of a flame does a goldsmith use for melting gold and silver and why ?


A goldsmith uses the outer zone (non-luminous zone) of candle flame to melt gold and silver because it is hottest zone and has more temperature.
 

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Make a labelled diagram of candle flame.


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