Green hydrogen, produced typically using electrolysis, can be used in various ways, specifying the validity of all three statements. Firstly, it can be utilized directly as a fuel in internal combustion engines. The hydrogen combines with oxygen to produce energy in a clean process, with water as the only by-product.

Secondly, this type of hydrogen can also be blended into natural gas pipelines. This blend can then be used for heat or power generation, providing cleaner alternatives to conventional natural gas-driven processes.

Lastly, green hydrogen can indeed serve as a fuel source in hydrogen fuel cell vehicles. These vehicles generate electricity from the reaction of hydrogen and oxygen within the fuel cells, producing only water vapor and heat as emissions.

Thus all three options (1-3) are appropriate uses of green hydrogen, making answer option 3 the correct one - that all three statements are correct.