Na⁺ is a cation, that is, an ion with a positive charge.
NH₃ has polar covalent bonds (due to the difference in electronegativity between nitrogen and hydrogen). According to the VESPR theory, it has a trigonal pyramidal shape with a lone pair. As a consequence, it has a net dipole moment and the molecule is polar.
The intermolecular forces between Na⁺ (ion) and NH₃ (dipole) are ion-dipole forces.
Anhydrous sodium carbonate is stable to heat and does not decompose even when it is heated to redness. This is because sodium carbonate salt on heating with acids react to release carbon dioxide.
