A soil with low PH value can be improved by the addition of

If a soil has a low pH value, it means it's acidic, which can make it difficult for plants to grow in. One way to improve the soil is by adding a substance that can neutralize the acidity and raise the pH level. Out of the options given, the substance that can best achieve this is calcium carbonate. Calcium carbonate is a basic compound that can react with the acid in the soil, producing carbon dioxide gas and water. This reaction helps to reduce the acidity in the soil and make it more alkaline, which is better for plant growth. The other options, like ammonium sulphate, sodium chloride, sodium nitrate, and magnesium phosphate, may have other benefits for plant growth, but they won't have the same effect on soil acidity as calcium carbonate.