How many genetic codons are considered stop codons (nonsense codons)?

Which of the following is the initiator codon?

How many amino acids will be coded by the $mRNA$ sequence $5'-CCCUCAUAGUCAUAC-3'$ if an adenosine residue is inserted after the $12^{th}$ nucleotide?

The number of possible alternative bases in the codons of amino acids is . . . . . . .

The degeneracy of the genetic code is due to the:

The sequence of a processed $m-RNA$ is given as $5'-AUG\ CUA\ UAC\ CUC\ CUU\ UAU\ CUG\ UGA-3'$. How many amino acids will be present in the polypeptide chain translated from this $m-RNA$?