Hint: The cell component visible only during cell division is a thread-like structure that is found inside the nucleus of the animal cell. There are 23 pairs of this structure present in humans.
The cell component visible only during cell division is the chromosome. In a nondividing cell, the genetic material that is known as DNA is present as chromatin fibers. Chromosomes are visible only during certain stages of cellular division. Chromosomes are formed by coiling and supercoiling of chromatin fibers. Since, during cellular division, chromosomes are highly condensed, they're visible under a microscope.
The chromosome is commonly known as a long molecule of DNA with part or all of the genetic material of an organism. It was seen that most of the eukaryotic chromosomes include protein which helps in packaging called histones which, aided by chaperone proteins, bind to and condense the DNA molecule to keep up its integrity. These chromosomes display a complex three-dimensional structure, which plays a big role in transcriptional regulation.
Chromosomes are found to be normally visible under a light-weight microscope only during the metaphase of cellular division (where all chromosomes are aligned within the center of the cell in their condensed form). Before this takes place, each chromosome is duplicated (S phase), and both copies are joined by a centromere, resulting in either in an X-shaped structure (pictured above), if the centromere is found equatorially, or a two-arm structure, if the centromere is found distally.
So, the correct answer is option (c) ‘ Chromosome’.
Note: As humans possess two copies of every chromosome, they even have two copies of every gene and locus on those chromosomes. Each of those trait-encoding genes (or loci) is named an allele. If the alleles match, the person is known homozygous for that trait.