Explanation:

- Commensalism: This is a relationship where one organism benefits while the other is unaffected. Classic examples include barnacles on whales or birds nesting in trees.

- Correct Answer: Option 2 - Commensalism

- Amensalism: Here, one organism is harmed while the other is unaffected. An example is a large tree blocking sunlight for smaller plants.

- Parasitism: In this relationship, one organism benefits at the expense of the other. Common examples are ticks on mammals or tapeworms in the intestines of animals.

- Mutualism: This involves both organisms benefiting from the relationship. A familiar example is bees pollinating flowers.