Question

what is the number of valence electrons of sodium carbonate?

Answer 1

Sodium carbonate is an compound and does not have valence electrons.

If you want to know about oxidation states of the constituent atoms they are as follows.

Na₂CO₃

CO₃ has -2 charge i.e. CO₃^-- oxidation states = 3xO = -6 (as O has -2 oxidation state) therefore C has +4 (-2 charge on the ion)

As Na always forms a Na⁺ ion, there are two Na ions in the compound. Oxidation state of Na = +1