Which position in a codon shows the greatest degeneracy? In other words, if a change occurs in this codon position, it is less likely to change the amino acid that is specified relative to the other positions.

Third position

Explanation:

Degenerate nature of genetic code refers to the fact that one amino acid can be encoded by more than one triplet combinations of nucleotides. However, if an amino acid is encoded by more than one triplets, the multiple triplets for that amino acid differ from each other with respect to the type of nucleotide present at the third position. For example,  isoleucine is encoded by AUU, AUC, and AUA. The third nucleotide is different in these genetic codes.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.