(a) The pH of soil Ais7.5 while that of soil B is 4.5. Which of the two soils A or B should be treated with powdered chalk to adjust its pH and why? (b) Name the chemical which is injected into the skin of a person: (i) During an ant’s sting. (ii) During the nettle leaf sting. How can the effect of these stings be neutralised? (c) Explain how the pH change in the river water can endanger the lives of aquatic animals like fish?

(a) The soil B with pH 4.5 is acidic. To neutralise this soil, it is treated with powdered chalk (CaCO₃). Acids react with chalk to form calcium salt. This reaction will neutralise the acidity of the salt.
(b) Ant’s sting and nettle leaf sting inject formic acid (methanoic acid) into the skin of a person. The effect of the sting can be neutralised by rubbrng with some alkaline substance like sodium bicarbonate or sodium carbonate.
(c) Aquatic animals are used to live in river water with a definite pH range. Whenever there is a change in the pH of water, it endangers the life of these organisms.