I think you forgot a picture so that someone can answer the question!
An ion usually has all of its electrons paired up whereas free radicals have one or more unpaired
The mass stays constant as it changes from a liquid to a solid
The answer for that would be C. this is because it is the only one where a base of the DNA was deleted. A. added another base to it, B. was exactly the same, and D. was a mutation of the DNA because it changed one part of it
Therefore, the answer is C
Hope this helped! :D