A Rep (repetition) is one complete motion of an exercise.
For example, if the teacher asks you to do 10 by 4 push-ups, then a "rep" would be your first 10 push-ups finished.
The volume percentage of solutions would indicate the relative abundance of a substance in a solution in terms of volume. This expression would be typically used for mixtures such as alcohol-water systems. This can be quantified by acquiring the ratio of the volumes of the substance of interest and the volume of the solution.
Can you clarify what your question is
The answer is c because protein is not oxygen