What is the approximate composition of the dry air by volume in the troposphere?

Question

Question ATPL - Airline Transport Pilot license - Meteorology

QuizVDS · Accepted Answer

21 % oxygen, 78 % nitrogen, and the rest other gasses

QuizVDS · Answer

88 % oxygen, 9 % nitrogen, and the rest other gasses

QuizVDS · Answer

10 % oxygen, 89 % nitrogen, and the rest other gasses

QuizVDS · Answer

50 % oxygen, 40 % nitrogen, and the rest other gasses

Id 121 - ATPL - What is the approximate composition of the dry air by volume in the troposphere?