Mine Gases - No. 15 Questions and answers taken from PowerPoint Presentations found on this site. Progress Indicator: Question 1 of 20 1.  What is hydrogen sulfide? Choices: A colorless, odorless, incombustible gas. A poisonous gas, yellow in color which is combustible. It is a poisonous, combustible, colorless gas having a taste and odor like rotten eggs. A non-poisonous, combustible gas with an odor like rotten eggs.