Concentrated acid and concentrated alkali are highly corrosive. They can corrode clothes and skin. They can spoil eyes if they go into the eyes. They are added slowly to water and turned into dilute solutions as they dissolve completely.

If by any chance, concentrated acids and concentrated alkali come into contact with your body, the spot must be cleaned time and again. Then you must inform your teacher.

We know strong acids provide more H+ in the aqueous solution than the weak acids. This excess amount of H+ conducts more electricity in the solution. That is why the bulb in a strong acid gives more light. On the other hand, the weak acid provides a lesser number of H+ in the aqueous solution resulting in a lesser amount of electrical conduction in the solution. So, the bulb gives less light.

An experiment with strong alkali (NaOH) and mild alkali (NH₄OH) will prove that the bulb in the solution of NaOH will give brighter light while the bulb in the solution of NH₄OH will give dim light. So, it proves that NaOH is strong alkali and NH₄OH is weak alkali.