We don't know what statement you want us to choose from. But, protons have a positive charge, and they are what makes an atom a certain atom.
Originally scientists believed in the plum pudding model of the atom (sphere of positive charge surrounded by smaller spheres of negative charge) then Rutherford did his scattering experiment (he shot alpha particles at a piece of gold foil some particles passed straight through the empty space of the atom, some were slightly deflected as they were closer to the atom's nucleus and some were completely reflected because they were headed in the path of the atom's nucleus
I believe it is D. because stoichiometry allows people to determine how much reactant is consumed in a chemical reaction.
The components are not permanently together. They can be separated and thats why its a mixture.