Question

Write any two observation in any activity which may suggest that a chemical reaction has taken place

Answer 1

1) Take Na2CO3 is a test tube and add a few drops of dil HCI to the test tube. A colourless and odourless gas is evolved which shows that chemical reactions has takes place. Pass the gas through lime water it turns lime water milky. 
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2) Take a bread and keep it outside for some days and after that you'll notice it will change its odour and smell?