Question

Some species of ant "farm" aphids by protecting them from predators. in return, the ants feed on a sugar-rich liquid (called honeydew) secreted by the aphids. the ecological relationship between the ants and the aphids is:

Answer 1

This was written poorly, but I assume you are talking about Commensalism:
"An association between two organisms in which one benefits and the other derives neither benefit nor harm."

Advantaged: ants
Neutral party: aphids