Why is a solution not a pure substance?
a. it is made up of 2 substances that are chemically combined,
b. the solute and the solvent cant be separated.
c. it is made up of one substance.
d. it is a mixture between a solute and solvent.

The answer is D .. it's a mixture between a solute and a solvent

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus. and thus finally, if we have the 32s2− ion, there are 18 electrons, 16 protons, and 16 neutrons.