"these two beakers represent solutions of hcl and naoh". describe a third beaker showing the ions that remain after the reaction has gone to completion.

Reacting solutions of HCl and NaOH in a third beaker will produce sodium chloride (NaCl), an ionic salt, and water (H₂O). The balanced chemical equation is:

HCl + NaOH → NaCl + H₂O

The third beaker would then show an aqueous solution since sodium chloride easily dissolves in water. The ions that would be present in the beaker are Na⁺ and Cl⁻ ions.   

The mass has escaped into a gas which you can not see so the law stays true.