A teacher performs a demonstration to show the properties of an unknown substance. The teacher cuts off a piece of gray shiny substance and drops it in water. The substance floats and reacts violently with the water. Based on this information, what type of element is the unknown substance?

Growing crops in places where major pests don't live using beneficial insects to eat harmful insects using a rat trap instead of a rodenticide developing drought-resistant tomato plants using beneficial insects or natural oils to repel pests planting a different crop every year to fake out the pests keeping food covered to deter ants and rodents developing bean plants with a resistance to fungus picking caterpillars off tomato plants cultivation practice biological control cultural control genetic resistance natural chemicals