What is the main component found inside the nucleus that contains DNA?

The main component found inside the nucleus that contains DNA is chromosomes. Chromosomes are structures made up of DNA tightly coiled around proteins known as histones. This organization allows for the efficient packaging of DNA within the nucleus and is crucial for the processes of cell division and gene expression. Each species has a specific number of chromosomes, which carry the genetic information necessary for the growth, development, and reproduction of the organism.

Other components mentioned in the choices serve different roles. For instance, ribosomes are responsible for protein synthesis, the nucleolus is involved in ribosome production, and the endoplasmic reticulum plays a key role in the synthesis of proteins and lipids. Therefore, while all of them are important cellular structures, chromosomes are specifically the entities that contain and organize the genetic material within the nucleus.