Solve all of this please

Dear student,

2) 
a) ​​​​​​A chemical reaction is a process that leads to the transformation of one set of chemical substances to another by changing the chemical composition of the substances.
It is a term used for depicting a change in which a substance (called reactant) decomposes, combines with other substances, or interchanges constituents with other substances to form new substances called products.

b) Necessary conditions for a chemical reaction to take place is- 

• Reactants should be present in close contact.
• Some substance reacts in the solution form.
• Some reactant needs some form of heat energy.
• Some reactions take place in the presence of light.

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