This research aims to explore the level of understanding of future teachers of physical sciences on the nature of charge carriers exchanged when the oxidation-reduction reaction takes place in an acid medium and to identify the types of reasoning that led to the answers they propose. This is in order to know if they have the cognitive resources necessary to approach with their future learners the concept of redox reaction according to the reaction medium. To do this, 585 student-teachers of physical sciences (physics and chemistry) from the first and second cycles of the higher teacher training college of Yaoundé were interviewed between 2015 and 2021. The results obtained in this research show that 61.54% of student-teachers questioned can’t identify the type of particles exchanged when the redox reaction takes place in an acid medium. This result leads us to conclude that most of the future teachers of physical sciences in Cameroon have a very low level of understanding of redox reactions in an acid medium and, therefore, do not have sufficient cognitive resources to help their future learners to better interpret oxidation -reduction reactions as a function of the reaction medium