The name for the ion (S_2O_9^{2-}) is disulfur nonaoxide.
The compound Na2N is called sodium nitride. It is an inorganic compound composed of sodium and nitrogen atoms.
What is the common name for a chalk?
The common name for a chalk is simply "chalk". It is a soft, white, porous sedimentary rock used for writing or drawing on blackboards or sidewalks.