The correct option is option 1: "A biotic community and its non-living elements."

An ecosystem refers to a specific area where living organisms, such as plants, animals, and microorganisms, coexist with their physical environment. Option 1 correctly states that an ecosystem consists of a biotic community and its non-living elements. The biotic community refers to all the living organisms within the ecosystem, while the non-living elements refer to the physical components of the environment, such as air, water, soil, and sunlight. Both the living and non-living components of an ecosystem are interconnected and depend on each other for survival. This option captures the fundamental components that make up an ecosystem.