Question

which atom is available to be picked up by producers?
a nitrogen atom in the soil
an iron atom in a rock
a sulfur atom in the air
a carbon atom in a cow

Explanation:

Plants (producers) can absorb nitrogen from the soil. Iron in rocks is not directly available. Sulfur in air is not in a form easily taken by producers. Carbon in a cow is part of an animal, not available for producers to pick up directly.

Answer:

A. a nitrogen atom in the soil