The question asks, "What is at the center of a cell?"
Answer: The nucleus. ✅
What is a nucleus?
A nucleus is the center organelle of a cell that stores DNA. DNA is interpreted to some as data, or instructions. These, "instructions" are often carried out by, "spheres with feet" as some people call them. Their real names are vescicles. They are like the mailmen of the cell, carrying out the instructions their boss, the nucleus, gives them, always making sure every other thing in the cell functions properly.