A plant is moving mineral ions from the soil into its roots by the process of active transport. Does this suggest that the concentration of ions is higher in the soil or the roots?

The concentration is higher in the soil. The process of active transport is used to move molecules against the concentration gradient (from a low to a high concentration). Therefore the concentration of ions must be lower in the soil than the roots.If the concentration of ions was higher in the soil then the plant could just rely on diffusion to move them into the roots. This is because molecules naturally like to move down the concentration gradient, from a high to a low concentration.