Which statement about the two chains of DNA is true?

The correct statement is that the two chains of DNA run in opposite directions. This characteristic is fundamental to the structure of the DNA double helix. Each strand of DNA has a directionality determined by the orientation of its sugar-phosphate backbone, which is described as running from a 5' end to a 3' end. In a DNA double helix, one strand runs in the 5' to 3' direction while the complementary strand runs in the opposite direction, from 3' to 5'. This antiparallel arrangement is crucial for the formation of base pairs and the overall stability of the DNA structure, allowing enzymes such as DNA polymerase to replicate the molecule accurately.

The other statements do not accurately reflect the structural properties of DNA. While it may seem intuitive to think of the chains as potentially being of equal length, they do not differ in this aspect; both strands are typically of the same length in a double-stranded DNA molecule. Additionally, the strands have complementary structures but are not identical due to their specific sequences of nucleotides. Thus, the antiparallel arrangement is essential for the functioning and integrity of DNA.