Which of the following statements is incorrect?

The correct answer is Option (2) → tRNA, then called sRNA (soluble RNA), became known after the genetic code was postulated.

Francis Crick saw that amino acids cannot read the code on their own, so some molecule must read a codon on one side and carry the matching amino acid on the other. He called it an adapter molecule. The tRNA fills this role: its anticodon loop pairs with the codon, and its acceptor end binds the amino acid.

Option (1) There are no tRNAs for the stop codons. — Correct statement. A stop codon (UAA, UAG or UGA) codes for no amino acid, so no tRNA carries an anticodon for it. The ribosome stops when it reaches one, and a release factor ends translation.

Option (2) tRNA, then called sRNA (soluble RNA), became known after the genetic code was postulated. — Incorrect statement. This is the changed line. The sRNA was known before the genetic code was postulated. What came much later was the finding that it works as the adapter molecule.

Option (3) The codon is read in mRNA in a contiguous fashion, and there are no punctuations. — Correct statement. The codons follow one another without any gap or spacer base. This is why adding or deleting one base shifts the reading frame.

Option (4) From bacteria to human, the codon UUU codes for phenylalanine. — Correct statement. This is the example NCERT gives to show that the code is nearly universal. Exceptions are found only in mitochondrial codons and some protozoans.

NCERT Extract:
tRNA – the Adapter Molecule – “From the very beginning of the proposition of code, it was clear to Francis Crick that there has to be a mechanism to read the code and also to link it to the amino acids, because amino acids have no structural specialities to read the code uniquely. He postulated the presence of an adapter molecule that would on one hand read the code and on other hand would bind to specific amino acids. The tRNA, then called sRNA (soluble RNA), was known before the genetic code was postulated. However, its role as an adapter molecule was assigned much later. … For initiation, there is another specific tRNA that is referred to as initiator tRNA. There are no tRNAs for stop codons.”
Genetic Code – “… (iii) The codon is read in mRNA in a contiguous fashion. There are no punctuations.
(iv) The code is nearly universal: for example, from bacteria to human UUU would code for Phenylalanine (phe). Some exceptions to this rule have been found in mitochondrial codons, and in some protozoans.”