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a)please explain a reason why fresh air cannot be regarded as pure substance? b)Electrolysis of water is a chemical change?
a, Pure substances are substances with only one type of constituent particles.Elements and compounds are pure substances.

Fresh air is a mixture of many gases like nitrogen,oxygen, carbon dioxide and dust particles. So fresh air is an example for mixture.

b, A chemical change is a permanent, not easily reversible change in which the identity of the substance is altered to produce one or more new substances.

Water is made up of one molecule of oxygen and two molecules of Hydrogen i.e. H2O .
By Passing electric current through water, oxygen and Hydrogen can be separated.

The newly formed substances have different properties than the original substances.


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