Question

what is the molecular formula of oxide of arsenic in its gaseous state (also I need to explain how this formula came about )??

There are two arsenic oxides. One is As2O3 and the other is As2O5. How did that come about? Please clarify. I assume you have some data; previous posters have had percent composition or grams to work with and the correct formula was determined from that. If that is the case with you please post all of your question. We can answer questions better if we know specificis and not generalities.