The electrovalency of sodium in NaCl is 

The number of  ${\mathrm{e}}^{-}$ that an atom loses or gains during the formation of ions is called Electro valency. For the formation of NaCl, Na losses one electron and becomes Na⁺.

 $\mathrm{Na}\to {\mathrm{Na}}^{+}+{\mathrm{e}}^{-}$