how many moles of Mg2+ and NO3(there is a negative sign on top of the 3 in NO3)form for each mole of Mg(NO3)2 that dissolves?

Answer 1

Mg(NO3)2 ==> Mg^2+ + 2NO3^-
Look at the equation. The equation tells you that you get 1 mol Mg^2+ and 2 mols NO3^- for every 1 mol Mg(NO3)2 that dissolves.