Final answer:
A single base-pair substitution in the third position (3rd) of a codon is most likely to lead to a silent mutation. This is because the third base of a codon is often considered the "wobble" base, and changes in this position may still allow the correct incorporation of the same amino acid into a protein.
Step-by-step explanation:
A single base-pair substitution in the third position (3rd) of a codon is most likely to lead to a silent mutation. This is because the third base of a codon is often considered the "wobble" base, and changes in this position may still allow the correct incorporation of the same amino acid into a protein. Silent mutations do not result in a change to the amino acid sequence of a protein and may go undetected unless the gene is sequenced.