What kinds of bonds can happen between the elements of a compound

What kinds of bonds can happen between the elements of a compound?

Covalent and Ionic

Gravity bc it’s gravity

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.