WAEC Agriculture 2022 Paper

Concept:The volume of air or pore space in a soil sample is found by comparing the expected total volume with the actual measured volume when soil and water are mixed.Explanation:When dry soil and water are mixed, the water fills the air spaces inside the soil.Therefore, the measured volume of the mixture becomes less than the simple sum of the two volumes.First, find the expected total volume if no air spaces existed:$$\text{Expected volume} = 52\,\text{cm}^3 + 48\,\text{cm}^3 = 100\,\text{cm}^3$$But the actual volume of soil and water together is only $78\,\text{cm}^3$.This decrease in volume is caused by the air spaces present in the soil.So, the volume of air space is:$$100\,\text{cm}^3 - 78\,\text{cm}^3 = 22\,\text{cm}^3$$This loss in total volume represents the air space in the soil sample.Answer:The volume of air space in the soil sample is $22\,\text{cm}^3$.Therefore, the correct option is A.