Melting temperature for double stranded molecules are converted into single stranded molecules. Which one of the following DNA will have the highest melting temperature?

The correct option is D DNA with $30$% cytosine
The stability of the DNA segment depends on the type of bases. If the DNA is rich in cytosine and guanine, then the DNA is considered to be more stable and have the highest melting point. The more the number of cytosine and guanine, the more are the hydrogen bonds and more stable is the DNA.

Thus, the correct answer is option B.