Assertion: Muton has fewer nucleotides than a cistron.
Reason: Benzer coined the term muton to the smallest unit of genetic material capable of mutational change.
A. Both assertion and reason are correct and the reason is the correct explanation for the assertion.
B. Both assertion and reason are correct but the reason is not the correct explanation for the assertion.
C. The assertion is correct but the reason is incorrect.
D. Both assertion and reason are incorrect.

Hint: The human genome consists of genetic information that is inherited from parents to off-springs. The chromosomes consist of functional segments called genomes. The genomes further consist of cistrons. The cistrons are made of many recon units and recons are further made of the smallest unit of the genome. Benzer coined an appropriate term for these smallest units that cause phenotypic change.

Complete answer:
The muton is the smallest unit of a gene. They are elements of one or more nucleotides long that can undergo mutations. They are not longer than a cistron. Benzer coined the term muton for these smallest lengths of DNA that can mutate to introduce changes in phenotypic characters. Thus, they are regarded as units of mutation in the genome. The genome is the building material of organisms that assists and directs the cells of the organism to work properly. The genome is present inside the nucleus of the cells. It contains the genetic information that is transferred from one generation to another. In human beings, the genome is made of 46 molecules of DNA that are called chromosomes. The chromosomes exist in pairs of 23. One pair comes from the maternal genome and the other comes from the paternal genome. This makes 46 chromosomes in the baby. The chromosomes contain around 30,000 genes that are functional units that encode for proteins. These proteins are responsible for the phenotypic expressions of an organism. The cistron is the largest segment of the gene that functions to encode for proteins during the transcription process. A cistron is a unit of function of a gene. The cistrons consist of recons. These are locations within a gene that performs recombination. Recombination occurs between recons within a gene. Thus, recon is a unit of recombination.
Hence, the correct answer is option A.

Note: Each recon consists of several mutons within them. Many mutons in a recon segment stay linked due to recombination. Due to this, a gene may have one or more than one cistron. Further, a cistron may have several recons that include several mutons.