Humus is an amorphous, colloidal, dark-coloured substance.
It is resistant to microbial action and contributes to soil fertility.
Light-coloured humus is not a characteristic feature.
If vector \( \mathbf{a} = 3 \hat{i} + 2 \hat{j} - \hat{k} \) \text{ and } \( \mathbf{b} = \hat{i} - \hat{j} + \hat{k} \), then which of the following is correct?