I want to say physical change? i’m not quite sure, i hope this helps tho!
C is the answer.
It says on the third picture that Bohr refined Rutherford's model by giving distinct orbits for the electrons with distinct radii.
An oxygen atom is 16x more massive than a hydrogen atom.
You can figure this out by comparing the atomic masses of the two elements: oxygen has an atomic mass number of 16, and hydrogen has an atomic mass number of 1. Thus, an oxygen atom is 16 times more massive than a hydrogen atom.
