The correct answer is option 2: A-2, B-4, C-3, D-1.

The question asks us to match a list of gases with their main chemical compositions. Let`s go through the options one by one to understand why option 2 is correct:

A. Water gas: Water gas is a mixture of carbon monoxide (CO) and hydrogen (H2). The main chemical composition of water gas is CO + H2. This matches with option 2, where A is matched with 2.

B. Producer gas: Producer gas is a mixture of carbon monoxide (CO) and nitrogen (N2). The main chemical composition of producer gas is CO + N2. This matches with option 2, where B is matched with 4.

C. Coal gas: Coal gas is a mixture of methane (CH4), carbon monoxide (CO), and hydrogen (H2). The main chemical composition of coal gas is CH4 + CO + H2. This matches with option 2, where C is matched with 3.

D. Gobargas: There is not enough information available about the main chemical composition of gobargas. However, it is not composed of CH4, CO, and N2,