A 1 kg soil sample has 2 cmol_c of Al³⁺ on the exchange complex.Addition of which of the following would most effectively replace about half of this Al?

Question

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The cation exchange capacity of the soil is 2 cmolc/kg. To replace half of this Al, we need to add an element with a valence of 2, which can replace 1 cmolc/kg of Al. Options A, D and E are all monovalent cations and hence would not be able to replace half of the Al. Option B is hydroxide, OH-, which has no charge, hence cannot replace Al. Option C, calcium (Ca2+), has a valence of 2 and can replace 1 cmolc/kg of Al, hence addition of 4 cmolc/kg of Ca would effectively replace half of the Al.

A 1 Kg Soil Sample Has 2 Cmolc of Al3+

A 1 Kg Soil Sample Has 2 Cmol_c of Al³⁺