(Solved): 7. Soils A, B, C and D were subjected to determination of exchangeable \( \mathrm{Ca}, \mathrm{Mg}, ...

7. Soils A, B, C and D were subjected to determination of exchangeable \( \mathrm{Ca}, \mathrm{Mg}, \mathrm{K}, \mathrm{Na} \) and acidity and the results are given in Table 1. Calculate CEC. Table 1. Soil analytical results \begin{tabular}{|l|r|l|l|l|r|l|l|} \hline Soil & \multicolumn{2}{|c|}{\( \mathbf{C a} \)} & Mg & K & Na & Acidity & CEC \\ Interpretation \\ \hline \multicolumn{8}{|c|}{\( \mathbf{c m o l}^{\prime} / \mathbf{k g} \)} \\ \hline A & 21 & 18 & 2.5 & 1.6 & 1.2 & & \\ \hline B & 4 & 3.8 & 4 & 3.2 & 0.25 & & \\ \hline C & 6.5 & 10 & 5 & 2 & 0 & & \\ \hline D & 0.75 & 1.2 & 2 & 1.5 & 2.1 & & \\ \hline \end{tabular}