Question

4. Mention any two observations which will help us to identify a given change as a chemical
reaction.
5. Name the gas liberated at cathode during electrolysis of water and how would you identify the
[1]
gas?​

Answer 1

4 a change in colour

b evolution of gas

c formation of new substance

5 hydrogen gas

we can check its presence by bringing a lighted matchstick toward it and it

will burn with pop sound.