Final answer:
Using Chargaff's rule, which states that the amount of adenine is equal to thymine and cytosine is equal to guanine in a DNA molecule, the number of thymine bases should be equal to the number of adenine bases. Given 15 cytosine bases, there are 10 remaining adenine/thymine base pairs out of 50 total base pairs. Thus, there should be 10 thymine bases, however, the answer options provided in the question do not include this number, suggesting a possible error in the question. Option number a is correct.
Step-by-step explanation:
If a double-stranded DNA molecule of 50 base pairs contains 15 cytosine bases (C), the number of thymine bases (T) it will contain can be determined using Chargaff's rule. This rule states that in DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). Since a DNA strand is complemented by another where each A complements a T and each C complements a G, the number of thymine bases should match the number of adenine bases, and the number of cytosine bases should match the number of guanine bases.
In this case, we have 15 cytosine bases (C); this means there would also be 15 guanine bases (G) because of their complementarity. This leads to a total of 30 bases (15 C + 15 G), which leaves us with a remainder of 20 bases for adenine (A) and thymine (T) combined (since there are 50 base pairs in total). Considering the rule where adenine always pairs with thymine, these 20 remaining bases must be equally divided between adenine and thymine bases. Thus, there would be 10 adenine bases and 10 thymine bases. The correct number of thymine bases in the DNA molecule is 10, which is not listed in the options provided, so the question might contain an error or is based on incorrect premises.