So here it says the lattice formation of magnesium bromide is the energy change for which of the following processes. So remember in a lattice formation reaction we have the ionic gases combining to form an ionic solid.
So here magnesium is in Group 2A so it's two plus boards charge so this is good. Bromine's in Group 7/8 so it's -1 so this is good. And then remember they combine together to form an ionic solid, not a gas. So this is out the answer.
The only answer that can work is option three. None of the others work because they don't have ions to begin with that combine to form an ionic solid. So here our answer would be choice C.