Assertion: A monocistronic mRNA can produce several types of polypeptide chains.
Reason: The terminator codon is present on the rRNA.
a.Both assertion and reason are correct and reason is the correct explanation for the assertion.
b.Both assertion and reason are correct and reason is the not correct explanation for the assertion.
c.Assertion is correct but reason is incorrect.
d.Both assertion and reason are incorrect.

Hint: Messenger RNA (mRNA) is a single-stranded RNA molecule that is complementary to one of the DNA strands of a gene.

Complete answer:
The basic role of mRNA is that it helps in a process known as protein synthesis. mRNA is a single-stranded molecule that carries genetic code from DNA in a cell's nucleus to ribosomes. The ribosome is the site of protein synthesis.

Option a: The monocistronic mRNA codes for only a single protein i.e. it can be translated to form only one type of protein and the terminator codon is also known as a stop codon. It does not code for any amino acid. So, assertion and reason are incorrect and reason is the not correct explanation for the assertion. Therefore, this is an incorrect option.

Option b: The monocistronic mRNA codes for only a single protein i.e. it can be translated to form only one type of protein and the terminator codon is also known as a stop codon. It does not code for any amino acid. So, assertion and reason are incorrect and reason is the not correct explanation for the assertion. Therefore, this is an incorrect option.

Option c: The monocistronic mRNA codes for only a single protein i.e. it can be translated to form only one type of protein and hence the assertion is incorrect. Therefore, this is an incorrect option.

Option d: Monocistronic mRNA is a type of mRNA that codes for only a single protein i.e., it can be translated to form only one type of protein. So, monocistronic mRNA can produce only one type of polypeptide chain. Hence, the assertion is incorrect. Terminator codon, also known as a stop codon, is a triplet of nucleotides present on mRNA that signals for the termination of translation i.e., the site at which synthesis of the polypeptide chain is terminated or stopped. Therefore, termination codons do not code for any amino acid. Hence, the reason is incorrect. Therefore, this is the correct option.

Hence the correct answer is option ‘d’.

Note:It is to be noted that ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes.We have remember that mRNAs have single initiation and termination sites and single type of polypeptide is produced.