Which of the following represents double-stranded nucleic acid?

The correct answer is DNA, which is the only option that consists of a double-stranded structure. DNA (deoxyribonucleic acid) is characterized by its double helix formation, where two strands of nucleotides are twisted around each other, connected by complementary base pairs. This double-stranded nature is crucial for its stability and function in storing and transmitting genetic information.

In contrast, RNA (ribonucleic acid) typically exists as a single-stranded molecule, playing various roles in protein synthesis and gene expression, but not exhibiting the double-stranded structure of DNA. Proteins, on the other hand, are not nucleic acids at all; they are made up of amino acids and perform a wide variety of functions within the cell, including catalysis, structure, and signaling. Ribosomes are cellular structures made up of ribosomal RNA and proteins, essential for synthesizing proteins, but they do not represent nucleic acids themselves. Therefore, the unique double-stranded nature of DNA makes it the correct answer for this question.