To determine which of the given compounds is organic, we need to understand what qualifies a compound as organic. Organic compounds generally contain carbon (C) atoms bonded to hydrogen (H) atoms and often include other elements such as oxygen, nitrogen, sulfur, and more.
Let's analyze each option:
1. Ammonia (NH\(_3\)):
- Ammonia consists of one nitrogen (N) atom and three hydrogen (H) atoms.
- Although it contains hydrogen, it does not contain carbon, which is a key element in organic compounds.
- Therefore, ammonia is not an organic compound.
2. Calcium sulfide (CaS):
- Calcium sulfide consists of one calcium (Ca) atom and one sulfur (S) atom.
- It lacks both carbon and hydrogen.
- Thus, calcium sulfide is not an organic compound.
3. Octane (C\(_8\)H\(_{18}\)):
- Octane consists of eight carbon (C) atoms and eighteen hydrogen (H) atoms.
- Since it contains both carbon and hydrogen in a bonded structure typical of organic compounds, octane is an organic compound.
- Therefore, octane is an organic compound.
4. Sulfur trioxide (SO\(_3\)):
- Sulfur trioxide consists of one sulfur (S) atom and three oxygen (O) atoms.
- This compound does not contain any carbon atoms, which are necessary for a compound to be considered organic.
- Consequently, sulfur trioxide is not an organic compound.
Among the given options, the compound that qualifies as an organic compound is octane (C\(_8\)H\(_{18}\)).
Therefore, the organic compound is option 3.
