What is the main function of the nucleus in a cell?

The main function of the nucleus in a cell is to control cell activities. The nucleus acts as the control center, housing the cell's genetic material in the form of DNA. This DNA contains the instructions necessary for the development, function, and reproduction of the cell. It regulates various cellular processes by controlling gene expression, which determines which proteins are made and when, thereby influencing the cell's structure and function. In this way, the nucleus directs all significant activities within the cell, including growth, metabolism, and response to stimuli, thereby playing a crucial role in maintaining homeostasis and enabling the cell to adapt to its environment.

Other options pertain to different organelles: packaging proteins is primarily the function of the Golgi apparatus, storing water and salts is typically associated with vacuoles, while energy creation is a function of mitochondria.