The question is a bit ambiguous. It's hard to tell what you're asking about without more context. Here are some possibilities and their explanations:

1. Gas released by a specific substance or process:

* Combustion: Burning things releases gases like carbon dioxide, water vapor, and nitrogen oxides.

* Decomposition: When certain substances break down, they might release gases like methane (from rotting organic matter) or hydrogen sulfide (from decaying eggs).

* Volcanic eruptions: Volcanoes release gases like sulfur dioxide, carbon dioxide, and water vapor.

* Cellular respiration: Living organisms release carbon dioxide as a byproduct of energy production.

2. Gas produced by a specific type of organism:

* Methane: Some microorganisms produce methane as a waste product.

* Hydrogen sulfide: Certain bacteria release hydrogen sulfide, which can have a rotten egg smell.

3. Gas naturally occurring in the atmosphere:

* Nitrogen: The most abundant gas in the atmosphere (about 78%).

* Oxygen: The second most abundant gas (about 21%).

To help me answer your question, please provide more information about:

* What kind of gas are you interested in?

* What is the context of this gas being "self-given off"? Is it a chemical reaction, a biological process, or something else?

With more details, I can provide a more specific and accurate answer.