Which two gases are most abundantly emitted in volcanic outgassing? a. nitrogen and oxygen b. hydrogen and helium c. carbon dioxide and methane d. water vapor and sulfur dioxide?

d. water vapor and sulfur dioxide?

As per result of studies done on volcanic eruptions, Water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2) are the most common volcanic gases abundantly emitted in volcanic outgassing. Other gases like carbon monoxide, methane and hydrogen are released in lesser amounts. 

water vapor and sulfur dioxide.

you did not give any options thus this is the best answer i can give to you with this little information you have given

> they are both natural and not man made

> they can be tracked and predicted by the right tools

-love shrooms