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.