In three-dimensional solid $Si{O}_2$, hybridization of Si is:

The correct option is C

Do you think it will be sp hybridized?
No, here that is not the case.
Why?

Silicon dioxide is a covalent, three-dimensional network solid in which each silicon atom is bonded to four oxygen atoms which are arranged tetrahedrally around it and each oxygen atom is attached to two silicon atoms by covalent bonds. Each corner is further shared by another tetrahedron.

The entire crystal may thus be considered as a giant molecule in which eight-membered rings are formed with alternate silicon and oxygen atoms.

So, C is the correct option.