The question asks about elements that cycle in the environment and have a gaseous phase at some point in their cycle. Let's analyze each option:

1. Phosphorus: The phosphorus cycle is mainly sedimentary, involving the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. It does not have a significant gaseous phase in its natural cycle.
2. Sulphur: The sulphur cycle includes a gaseous phase. Sulphur is released into the atmosphere as hydrogen sulfide (H₂S) and sulfur dioxide (SO₂), making it a part of its natural cycle.
3. Carbon: Carbon has a prominent gaseous phase in the form of carbon dioxide (CO₂) and methane (CH₄). It is essential in the carbon cycle through processes like photosynthesis and respiration.

Given this information, the correct answer is b only because only sulphur involves a definite gaseous phase in its environmental cycle among the given options.