The correct answer to this question is option 1: water gas. Water gas is the mixture of carbon monoxide (CO) and hydrogen gas (H2) that is formed by the action of steam on hydrocarbons. This process is known as steam reforming or the water gas reaction.

Option 2: producer gas is not the correct answer. Producer gas is a different mixture of gases that is produced by the incomplete combustion of carbonaceous materials, such as coal or biomass. It typically contains nitrogen, carbon monoxide, hydrogen, and methane.

Option 3: industrial gas is a vague term and does not specifically refer to the process of steam reforming or the formation of water gas.

Option 4: fuel gas is also not the correct answer. While water gas can be used as a fuel, the term fuel gas typically refers to a broad category of gases that are used as a source of energy, such as natural gas, propane, or butane.

Therefore, water gas is the specific term used to describe the mixture of CO and H2 gas that is formed by the reaction of steam with hydrocarbons.