The nucleus contains chromosomes, which appear as rod-shaped structures only when the cell is about to divide. These chromosomes are composed of _____.

The correct option is DNA and proteins.

Chromosomes are highly organized structures found inside the nucleus of eukaryotic cells. They carry the genetic information necessary for the growth, development, and reproduction of an organism. The structure of chromosomes consists of two main components:
1. DNA (Deoxyribonucleic Acid): This is the genetic material that stores the instructions required to build and maintain the organism.
2. Proteins: The long DNA strands are extremely long and must be tightly packed to fit inside the microscopic cell nucleus. Specialized proteins called histones act as spools around which the DNA wraps. This DNA-protein complex is known as chromatin, which condenses further into visible rod-shaped chromosomes when the cell prepares to divide.

Therefore, chromosomes are composed of DNA and proteins.