2a Just alternate + - + - (if one position is +, then its top, bottom, right, left, front and back if there is any are all-)

b Because the ions are stuck in that lattice and cannot move; the ions must move to be able to transfer electrical charges for electrical conduction

c Mg and O are 2+ and 2-
Na and Cl are 1+ and 1-

There are more attractions in 2+ 2- than 1+ and 1- (more discrepancy in pluses and minuses), so more energy is needed to overcome these electrostatic attraction forces

1 MgO CuSO4 NH4Cl CaCl2

For 2a, I meant alternate black dots and white dots