Question

what causes the centre of earth to have gravitational force?

Answer 1

$\huge\underline\green{Answer:-}$

At the very center, the gravitational force is zero because there's equal mass pulling on you from all sides, and it all cancels. If you built a room there, you could float around freely. That's what it means to say that gravity is zero at the center of Earth. However, the gravitational well is a different story.