Question

During electrolysis of water how can we identify the gas present in each test tube

Answer 1

The gaseous products of the electrolysis of water are hydrogen and oxygen. There are two ways one can identify the gas product in the test tubes:
1)Direct observation: since the ratio of the production of hydrogen : oxygen is        2:1 hence the gas with the most volume will be hydrogen and the one with the smaller volume, oxygen.
2) Use of a burning flame: when the test tube containing oxygen is introduced  to the flame, it will burn with a glow. Hydrogen on the other hand will burn with a pop sound.

Answer 2

Answer: During electrolysis of water hydrogen and oxygen gas is produced.

Explanation: CASE - 1

We can identify it by checking anode and cathode at anode oxygen atoms are situated and at cathode hydrogen atoms are situated.

CASE - 2. We can place burner and burns each test tube , we can see that in that test tube where pop sound is produced hydrogen is located there , and where pop sound is not produced oxygen is there.