Multiple choice Which of the following is the most abundant gas emitted from volcanoes? Water vapour Helium Sulphur dioxide Carbon dioxide Reveal answer Fill a bubble to check yourself A Correct answer Explanation Water vapor (H2O) constitutes about 60-90% of all volcanic gas emissions by volume. While CO2 and SO2 are significant, water vapor is by far the most abundant. Helium is present only in trace amounts. This makes option A correct.