How Many Different Kinds of RNA Codons Encode Amino Acids

Question

How many different kinds of RNA codons encode amino acids?  
A) 3
B) 72
C) 61
D) 64
E) 120

Accepted Answer

There are a total of 64 possible RNA codons, out of which 3 (UAA, UAG, and UGA) do not encode amino acids and serve as stop codons. This leaves 61 codons that encode the 20 different amino acids used to build proteins.