Which is most likely a covalent compound?

O

LIF

Mgs

NH3

CaCl2

O is not a compound.

LiF is a compound which contains a metal so is not likely to be a covalent compound.

Mgs involves a metal so it is not likely to be a covalent compound.

NH₃, both N and H are non metallic so it is likely to be a covalent compound.

CaCl₂ is not likely to be a covalent compound as it also contains metal.