A) hygrometer B) barometer C) thermometer D) ruler (More)QuestionNot AnsweredUpdated 7/3/2013 4:14:39 PM1 Answer/CommentandrewpallarcaMThe instrument used to determine air pressure is called a BAROMETER.Added 7/3/2013 4:14:39 PMRated good by StingAir is composed of nitrogen, oxygen, argon, carbon dioxide, and other gasses.