What type of nucleic acid is involved in protein synthesis and consists of single-stranded molecules?

RNA, or ribonucleic acid, plays a crucial role in the process of protein synthesis and is characterized by its single-stranded structure. In the context of protein synthesis, RNA serves as a messenger that carries the genetic information from DNA to the ribosomes, where proteins are synthesized. Specifically, messenger RNA (mRNA) is transcribed from DNA and then translated into a sequence of amino acids to form a protein.

The structure of RNA is distinctly different from DNA, which is double-stranded and contains the deoxyribose sugar. Protein, while essential in biological functions, is not a type of nucleic acid and is the final product of the protein synthesis process. Chromosomes, on the other hand, are complex structures made of DNA and proteins, containing the genetic material of an organism but do not directly participate in the protein synthesis process as single-stranded molecules.

Thus, the single-stranded nature of RNA is fundamental to its function in protein synthesis and distinguishes it from DNA and other options provided, making it the correct choice in this context.