To solve this exercise it is necessary to use the concepts related to Difference in Phase.
The Difference in phase is given by

Where
Horizontal distance between two points
Wavelength
From our values we have,


The horizontal distance between this two points would be given for

Therefore using the equation we have




Therefore the correct answer is C.
C. The number of F atoms in the reactants equals the number of F atoms in the products.
Answer:
first number is 113 and the second number is 15
I think that this is false but I am not sure