Sometimes the Sequence of DNA Gets Mutated and an Adenine

Multiple Choice

Sometimes the sequence of DNA gets mutated and an adenine is paired to a cytosine. Why is this interaction unstable?

A) Because the phosphate groups of the two bases repel each other.
B) Because an ionic bond cannot be formed between the two.
C) Because the chemical groups that form hydrogen bonds are in the wrong positions.
D) Because the charges on the bases repel one another.