Final answer:
Grasslands are likely to have the most fertile soils with a high accumulation of minerals due to the dense roots and rhizomes of grasses that nourish the soil.
Step-by-step explanation:
The area likely to have soil with the greatest accumulation of minerals available for plant growth among the options provided is the grasslands. Grasslands have fertile soils because the subsurface is packed with the roots and rhizomes of dense grasses, which anchor plants to the ground and replenish the soil's organic material when they die and decay.
In contrast, desert regions have sparse vegetation and lower organic matter, rainforests have rapid decomposition that can lead to nutrient-saturated soils that may wash away quickly, and mountainous regions often have thinner soils due to steep slopes and less organic material accumulation.