Which of the following statements regarding DNA and RNA is true?

DNA can melt while RNA cannot.

DNA is resistant to alkaline hydrolysis while RNA is not.

DNA contains phosphodiester bonds while RNA does not.

DNA can form double helices while RNA cannot.

To determine which of the statements is true, we can break down each statement and analyze it one by one.

1. DNA can melt while RNA cannot.
DNA melting refers to the separation of double-stranded DNA into single strands upon heating. RNA can also undergo a similar process called denaturation, where the hydrogen bonds holding the molecules together are disrupted, resulting in the separation of the strands. Therefore, this statement is incorrect.

2. DNA is resistant to alkaline hydrolysis while RNA is not.
Alkaline hydrolysis is the process in which DNA or RNA is degraded under alkaline conditions. DNA is generally more resistant to alkaline hydrolysis compared to RNA. Therefore, this statement is correct.

3. DNA contains phosphodiester bonds while RNA does not.
Both DNA and RNA consist of nucleotides that are connected by phosphodiester bonds. These bonds link the sugar-phosphate backbone of the DNA and RNA strands. Therefore, this statement is incorrect.

4. DNA can form double helices while RNA cannot.
DNA is known for its characteristic double helix structure, where two strands twist around each other. RNA, on the other hand, can form complex secondary structures, like hairpins and loops, but it does not typically form stable double helices. Therefore, this statement is correct.

Based on the above analysis, the correct statement is: DNA is resistant to alkaline hydrolysis while RNA is not.