We should brush our teeth twice a day as bacteria present in the mouth produce acids by degradation of sugar and food particles that remain in the mouth after eating. The best way to prevent this is to clean the mouth using toothpaste which is generally basic. These can neutralise the excess acid and prevent tooth decay.

Copper and brass vessels on reacting with acids get corroded. Kalai prevents their corrosion.

Take some turmeric and mix it in some water to make a paste. Deposit it on blotting paper of filter paper and dry it. Cut thin strips of the yellow paper so obtained. These thin strips are turmeric paper

The most commonly used natural indicator is litmus. It is extracted from lichens. It has a purple colour in distilled water. It is available in the form of a solution or in the form of strips of paper. It is available as red and blue litmus paper.

Phenolphthalein indicator is generally used in neutralization reaction.

Vegetable stain is due to turmeric which gives reddish brown colour with base (presence of soap solution).

Stomach contains hydrochloric acid

The effect of an ant bite can be neutralised by rubbing moist baking soda.

Carbonic acid.

Turmeric stain on white shirt is turned to red when it is washed with soap because the soap solution is basic in nature.

Milk of magnesia which contains magnesium hydroxide (base) is used to neutralise the effect of excessive acid in stomach.

The citric acid in lemon juice and oxalic acid in tomato.

(i) Turmeric
(ii) China rose

The solutions or substances which do not change the colour of either red or blue litmus paper are neutral.