Which one of the following is water gas ?

Water gas is an industrial fuel gas primarily composed of a mixture of carbon monoxide (CO) and hydrogen (H2) [3]. It is produced by passing steam over red-hot carbonaceous materials, such as coke or coal, at high temperatures [3]. This endothermic reaction (C + H2O → CO + H2) results in a gas mixture with high combustible content. It is often referred to as synthesis gas or syngas, particularly when used as a precursor for chemical synthesis [2]. In contrast, producer gas is a mixture of carbon monoxide and nitrogen, formed by passing air over red-hot fuel, where the nitrogen from the air remains as a diluent [1]. While water gas consists almost entirely of combustible components (CO and H2), producer gas contains significant non-combustible nitrogen.

Sources

1. [1] https://www.uspto.gov/web/patents/classification/cpc/pdf/defC10J.pdf
2. [2] https://en.wikipedia.org/wiki/Water_gas
3. [3] https://www.sciencedirect.com/topics/engineering/producer-gas