How is acid rain formed ?


Most of the, vehicles on the road and industries emit out gases like oxides of nitrogen and sulphur. Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to formmore acidic pollutants, known as acid rain.

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What should be done to control fire due to oils ?


In case of fire due to oils, water is not useful as it is lighter than oil and settles down below the oil particles. In such cases, sand or soil should be used. They cut off the supply of air to the fire and it is put off.

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How does water help in extinguishing the fire ?


Water helps in extinguishing the fire in two ways :

(i) It brings the temperature of the combustible material below its ignition temperature. As a result, the fire gets extinguished.

(ii) The water vapour formed due to the heat of fire cuts to supply of air. Due to the absence of air (supporter of combustion), the fire gets extinguished.

 

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State two disadvantages of incomplete combustion.


(i) Incomplete combustion of a fuel produces a poisonous gas called carbon monoxide and unburnt carbon particles which cause pollution. 

(ii) Incomplete combustion of a fuel produces less heat and hence leads to the wastage of fuel.

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The wick in a spirit lamp does not burn while the spirit in it burns. Give two reasons for the wick not burning.


The wick in a spirit lamp does not burn while the spirit in it burns because:

(i) The ignition temperature of wick is higher than that of spirit.

(ii) The heat produced by the burning of spirit is quickly transferred to the surroundings and, therefore, the temperature of wick remains below its ignition temperature.

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