Wasp sting inject a liquid in the skin which is acidic in nature. Hence, bakil]g soda is the appropriate remedy as it is basic in nature and neutralises the acid.

Nature of solution is given below:

Characteristics of acids are
(i) They are sour in taste.
(ii) They turn blue litmus paper/solution to red.
(iii) Dilution of acid in water is an exothermic reaction, i.e. heat energy is evolved.

(a) We take an antacid tablet such as milk of magnesia to neutralises the excessive acid released in the stomach.
(b) When an ant bites, it injects the formic acid into the skin. The effect of acid can be neutralised by applying calamine solution that contains zinc carbonate.
(c) The factory wastes contain acids if they are allowed to flow into the water bodies, the acid will kill fishes and other organisms. The factory wastes are thus neutralised by adding basic substances.

Dorji will decide which drink is to be served to whom (customer) by doing the following litmus paper tests:
(i) If the drink turns blue litmus paper to red, then the drink is acidic and hence will be served to the first customer who wants the acidic drink.
(ii) If the drink turns red litmus paper to blue, then the drink is basic and hence will be served to another customer who wants the basic drink.
(iii) If the drink shows no change in colour with litmus paper, then it will be neutral drink. Thus, it will be served to the third customer.
Since the soft drinks are edible. Dorji can take the decision by tasting the drinks. Acidic drinks will be sour to taste whereas basic drinks will be bitter to taste and neutral drinks will have no taste.

(a) All indicators do not change colour with acids as well as bases, e.g. turmeric changes its colour to pink with the base but it remains yellow with acid.
Therefore, statement (i) is incorrect. There are some indicators which change colour with both acid and base, e.g. methyl orange, litmus, thus statement (ii) and (iii) are also incorrect. Statement (iv) is the correct conclusion about indicators.

Neutralisation reaction.

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.

Acids turn blue litmus paper red while bases turn red litmus paper blue.

China rose (gudhal) is an acid-base indicator.
China rose solution in different medium shows following changes:
China rose + acid \(\longrightarrow\) Give dark pink colour, hence A is an acidic solution.
China rose + base \(\longrightarrow\) give green colour, hence B is a basic solution.
China rose + neutral \(\longrightarrow\) No change in colour, hence C is a neutral solution.

The reason for low crop yield in farmer's field was that the soil at a place is either too acidic or too basic. The soil may be acidic or basic naturally. The excessive use of fertilisers in the fields also makes the soil too acidic. When the soil is too acidic, it is treated with base such as quicklime (calcium oxide) or slaked lime (calcium hydroxide) which neutralises the excess acid present in the soil and reduces its acidic nature. If the soil is too basic, then decaying organic matter (called manure or compost) is added it. The decaying organic matter releases acid which neutralises the excess bases present in the soil and reduces its basic nature.