Question

corundum is the second - hardest mineral on the mohs hardness scale. how does this property make corundum useful to humans?
a. it means corundum can be used to make fireworks yellow.
b. it means corundum can be used as pencil lead.
c. it means corundum can be used to flavor foods.
d. it means corundum can be used to grind down and shape fingernails.

Explanation:

Corundum's hardness (second - hardest on Mohs scale) makes it useful for grinding and shaping. Pencil lead (graphite) is soft. Flavoring foods is about chemical properties (not hardness). Making fireworks yellow is about chemical composition (not hardness). Grinding and shaping (like in nail - shaping tools) uses its hardness.

Answer:

D. It means corundum can be used to grind down and shape fingernails.