The majority of the mass of the atom is located in the nucleus. Remember that the nucleus contains both protons and neutrons and therefore, most of the mass of the atom.
Using the significant figure it would be 27.3
The answer is salt water.
Salt water can conduct electricity or we can say that an electric current is conducted by salt water as salt water is a good conductor of electricity when salt that is sodium chloride or NaCl is dissolved in water , positively charged sodium (Na⁺) and negatively charged chlorine(Cl⁻) molecules are set apart by the water molecule so that they can float easily and freely. We can define the conductivity of a substance as the mobility or movement of ions. So as in water, sodium and chlorine are set apart and can move freely so it become a electrolyte that can conduct electricity.
To find the net ionic equation we must first write the balanced equation for the reaction. We must bear in mind that the reagents Ca(NO3)2 and Na2S are in the aqueous state and as product we will have CaS in the solid state, since it is not soluble in water and NaNO3 in the aqueous state.
The balanced equation of the reaction will be:

Ca(NO3)2(aq) + → Ca(aq) + 2Na(s)NO3Now, c(aq)ompounds in the aqueous state can be written in their ionic form, so the reaction will transform into:Na2S +

So, the answer will be option A