Final answer:
A free-living organism is the opposite of a parasitic organism, as it does not rely on another for its survival in a detrimental manner. The interaction where one benefits and the other is unaffected is known as commensalism. Therefore, the correct option is B.
Step-by-step explanation:
A free-living organism could be considered the opposite of a parasitic organism. Organisms involved in a parasitic relationship are in a symbiotic interaction where one species, the parasite, benefits at the expense of the other, the host, which is harmed. Conversely, free-living organisms do not rely on another species for their survival in such a close, long-term relationship.
To address the related question, the type of interaction between two prokaryotic populations in which one population benefits and the other is not affected is called commensalism. In this symbiotic relationship, one species gains a benefit, such as transportation or shelter, without affecting the other species negatively or positively.