Answer 1

George Gamow proposed that if 20 amino acids are to be coded by 4 bases, then the code should be made up of three nucleotides. 

43 = 64 (42 = 16), which is less than 20; so, the codon was proposed to be a triplet.

Har Gobind Khorana developed a chemical method to synthesize RNA molecules with a defined combination of bases.

Marshall Nirenberg developed cell-free systems for protein synthesis, which helped the code to be deciphered.

Severo Ochoa discovered an enzyme (polynucleotide phosphorylase) which helped in the synthesis of RNA with defined sequences in a template-independent manner.