Final answer:
The number of "letters" in an RNA molecule that provides the code for a single amino acid is three, as they make up a codon. Carbon chains can vary significantly in organic molecules, with simple organic molecules often displaying a range from two to several dozen carbon atoms.
Step-by-step explanation:
To answer the question about the number of "letters" in an RNA molecule required to code for a single amino acid, we refer to the basic unit of the genetic code—the codon. A codon consists of three nucleotides in sequence on an RNA strand. Each triplet of nucleotides, or a codon, corresponds to a specific amino acid or a stop signal during protein synthesis. Therefore, the correct answer is C. 3.
Regarding the chain length for carbon (carb) in molecules, carbon chains can vary greatly in length, from one carbon atom to many thousands, especially in the case of polymers and biologically formed chains like DNA and RNA. However, simple organic molecules often have carbon chains ranging from two to several dozen carbon atoms. The example given shows a molecule with a five-carbon chain.
In summary, RNA codons are composed of three nucleotides and carbon chains can vary in length significantly depending on the molecule in question.