Southwest Regional First Aid Exam Taken from the 2019 Southwest Regional Mine Rescue Contest held in Ruidoso, New Mexico Progress Indicator: Question 5 of 30 5.  Which of the following properties are associated with Hydrogen Sulfide gas: Choices: The gas is one of the most poisonous known. The gas is not soluble in water. The gas is yellowish, with an odor of rotten eggs. All of the above.