# Why has na 1S0 term Ag symmetry?

This question is a continuation of Molpro - Connection between atomic term symbols and system symmetry.

In the Feodoran's answer I found it somehow confusing, that $${}^1S_0$$ term should be totally symmetric. Or better said, I see no way, how to determine that.

So, my question is - how is $${}^1S_0$$ term connected with the atom symmetry?