Materials needed: Four test tubes, blue litmus papers, water, benzene, dilute Sodium hydroxide, dilute hydrochloric acid.

1. Take the test tubes and clean them.
2. take 5ml of water, 5ml of benzene, 5ml of sodium hydroxide and 5ml of hydrochloric acid in the four test tubes.
3. Take one blue litmus paper and insert it into first test tube.
4. See if the colour changes to red. If it changes to red, then it is an acid otherwise it is not an acid.
5. Repeat step 3 and 4 with rest test tubes.

You will see that the colour changes only in case of hydrochloric acid. The rest compounds don't change the blue litmus into red. So they are not acids though all of the compounds contain hydrogen.
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