The major combustible component of gobar (cow-dung) gas is methane. It is the primary gas released during the anaerobic digestion of cow dung. Methane is a hydrocarbon gas and is the main component of natural gas. It is highly flammable and can be used as a fuel for heating, cooking, and electricity generation.

Option 2: Carbon dioxide is not the major combustible component of gobar gas. While it may be present in small quantities, it is not the main component that contributes to its flammability.

Option 3: Hydrogen is not the major combustible component of gobar gas. While it may be present, it is not the primary gas released during the anaerobic digestion of cow dung.

Option 4: Propane is not the major combustible component of gobar gas. Propane is a different gas that is commonly used as a fuel for heating and cooking, but it is not a significant component of gobar gas.

In conclusion, the correct answer is option 1, methane, as it is the major combustible component of gobar gas.