Final answer:
For a DNA molecule with 10% cytosine, it has 10% guanine to comply with Chargaff's rules. As adenine and thymine also occur in equal amounts, the molecule has 40% adenine and 40% thymine.
Step-by-step explanation:
According to Chargaff's rules, in the DNA molecule, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). Therefore, if a DNA molecule contains 10% cytosine, it must also contain 10% guanine to satisfy the G=C rule. Consequently, the remaining 80% of the DNA must be composed of adenine and thymine in equal amounts, so each would be 40%. Therefore, the correct answer is: 40% guanine and 10% adenine.
To further elaborate, if 30% of the bases within a DNA molecule are adenine, due to Chargaff's rule stating A=T, the percentage of thymine would also be 30%. And if a different DNA sample contains 22% thymine, the amount of adenine would also be 22% to maintain the A=T balance, leaving the rest of the percentage to be divided equally between guanine and cytosine as per the G=C rule.