What is contained within the nucleus of a cell?

The nucleus of a cell is primarily known for housing the cell's genetic material, which is DNA (deoxyribonucleic acid). DNA carries the instructions essential for the functioning and reproduction of the cell. It is organized into structures called chromosomes and plays a critical role in cell division, gene expression, and the overall regulation of cellular activities.

While proteins, chlorophyll, and ribosomes are important components in various cellular processes, they are not contained within the nucleus in the same way that DNA is. Proteins are synthesized in the cytoplasm and can also be found within organelles; chlorophyll is specific to plant cells and is found in chloroplasts, not the nucleus; ribosomes, which are essential for protein synthesis, are also located in the cytoplasm or can be attached to the endoplasmic reticulum, rather than within the nucleus itself. Thus, the correct answer highlights the nucleus's primary function as the repository of genetic material.