Which one of the following codons performs a dual function?

AUG

The correct answer is Option (2) → AUG 

The function of AUG in the context of genetic coding is:

It codes for Methionine (Met) and  it  act as initiator codon.

AUG is known as the start codon and also codes for the amino acid Methionine in the genetic code. It serves as the initiation signal for protein synthesis, marking the starting point for translation and the incorporation of Methionine into the growing polypeptide chain during protein synthesis. UAA, UAG, UGA are stop terminator codons.