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Solution


Q.

Which one of the following processes involves a chemical reaction
1 Liquification of air  
2 Heating copper wire in presence of air at high temperature  
3 Keeping petrol in a china dish in the open  
4 Storing of oxygen gas under pressure in a gas cylinder  

Ans.

(2)

A physical change is the one in which the chemical properties of a substance do not change.
No chemical change is observed when we store oxygen gas under pressure, or during liquefaction of air, or when petrol is kept open in a china dish.
However, when we heat a copper wire in the presence of air, copper oxide is formed.

The reaction is as follows: 2Cu(s)copper+O2(g)oxygen→Heat2CuO(s)ccopper (ii) oxide

Thus, heating of copper wire in presence of air at high temperature is an example of a chemical reaction.