If the soil is acidic (PH < 7), then such soil should be treated with quick lime [calcium oxide(CaO)] or slaked lime [calcium hydroxide(CaOH)2] or chalk [calcium carbonate(CaCO3)].
Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide), or chalk (calcium carbonate)?