Clownfish live in sea anemones, which protect the fish from predators. the sea anemone isn't harmed and doesn't benefit from this relationship. this is called
parasitism
commensalism
phoresy
mutualism

The answer is commensalism.

Commensalism is a relationship between two organisms in which only one of them has benefit, and the other one is not affected (it has no harm or benefit).
In this example, clownfish has the benefit - it is protected from predators by sea anemones. The sea anemone isn't harmed and doesn't benefit from this relationship. Hence, this is the example of commensalism.

Commensalism

In this type of relationship, one organism benefits and the other is neither harmed nor benefited. 

B.) nitrogen fixationnitrogen fixation is the process of nitrogen molecules seeping into the soil and inside plant roots and bacteria. it gives more "life" to plants