The right answer is 5.
To answer this question, we must think in the same way as the demonstration showing that codons of 3 are necessary to encode an amino acid (in terrestrial species).
To calculate the number of nucleotides in a codon in these new species: we should use the law of:
nucleotides existing ^ (number of nucleotides in a codon) = number of codons. (in order to have the number of possible codon combinations)
The number of codons must be greater than or equal to the number of amino acids (17).
2 ^ 1 = 2 (<17)
2 ^ 2 = 4 (<17)
2 ^ 3 = 8 (<17)
2 ^ 4 = 16 (<17)
2 ^ 5 = 32 (> 17)
32> 17 so the number of nulceotides in a codon must be 5.
