Which element can toxic to plants growing in soils that are high acidity?

In acidic soils (low pH), aluminium becomes soluble and toxic to plant roots, inhibiting root growth and nutrient uptake. This is a major problem in agriculture on acidic tropical soils. Other options like carbon, zinc, and iron are either not typically toxic in these conditions or essential micronutrients. Aluminium toxicity is a well-documented issue in soil science.