Sodium and calcium do not pair because

They are both electropositive

Explanation:

Sodium and Calcium are both metals and therefore they are electropositive.

Both of them have large atomic radius and are willing to lose electrons instead of gaining or sharing of electrons.

To attain stability, both sodium and calcium must lose electrons. So there is no attraction between them to form bonds.

i don't see a text, but i am gonna assume this *orbit* the curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, as the sun.