Answer:
NaS is ionic compounds that's why it is polar.
Step-by-step explanation:
Ionic bond:
It is the bond which is formed by the transfer of electron from one atom to the atom of another element.
Both bonded atoms have very large electronegativity difference. The atom with large electronegativity value accept the electron from other with smaller value of electronegativity.
For example:
Sodium sulfide is ionic compound. The electronegativity of sulfur is 2.58 and for sodium is 0.93. There is large difference is present. That's why electron from sodium is transfer to the sulfur. Sodium becomes positive and sulfur becomes negative ion. There are electrostatic fores present between bonded atoms and molecule becomes polar.