In the genetic code dictionary,how many codons are used to code for the $20$ amino acids?

Khorana and his colleagues synthesized an $RNA$ molecule with a repeating sequence of $U$ and $G$ nucleotides. The $RNA$ sequence "$UGU\ GUG\ UGU\ GUG$" produced a tetrapeptide with alternating chains of cysteine and valine. The codons for cysteine and valine are, respectively:

Select the correct statement with respect to the Wobble hypothesis.

Which one of the following statements is not correct?

The genetic code is present on ........

Select the correct option for George Gamow.