One of the questions early geneticists had to answer was how only four nucleotides can specify placement of 20 amino acids in proteins. Today we know that , a sequence of three adjacent nucleotides, determine the insertion of a specific amino acid in a polypeptide chain.

Explanation:

The sequence of DNA is transcribed into mRNA, containing the sequence  for protein synthesis, protein is synthesized according to the codons in mRNA.  This sequence of nucleotide on DNA/ RNA is divided into a series of three nucleotide units, and one unit of three nucleotide is  known as codons.

There are overall 64 codons, 61 codons out of 64 codons, codes for overall 20  amino acids, and the remaining three  are stop codons.

These there codon do not code for any amino acid.

And these 61 codons, they  code for total 20 amino acids. So one amino acid can be coded by one or more than one codons.

2

Explanation:

valence electrons=reaction