Concept:Nitrogen deficiency is corrected by adding a nitrogen-containing fertilizer to the soil.Explanation:Maize needs nitrogen for healthy leafy growth and chlorophyll production.Sulphate of ammonia, (NH4)2SO4, is a nitrogen-rich fertilizer.Potassium chloride and muriate of potash mainly supply potassium, not nitrogen.Calcium carbonate supplies calcium and reduces acidity, so it does not provide nitrogen.Hence, the deficiency is best corrected with sulphate of ammonia.Answer:C. sulphate of ammonia