please explain how to solve!!!-thanks

**Answer 1**

A) We can tell that X have an outer valence shell of 1 because you “cross over” the valency to create the bond

EG: [X] + [PO4]3- -> X3PO4

Therefore X needs an outer shell of 1+ which is found in group 1, the alkaline metals

B) Much the same as the first section if you “cross over” the valency you have

EG: [Ca]2+ + X -> CaX2

Therefore X must need 2 electrons to gain a full valence shell and will be in group 17

C) If you cross over the numbers you have

EG: [X]3+ + [SO4]2- -> X2(SO4)3

Therefore X has a valence of 3+ and therefore would be put into group 13

This is my interoperation of this, however I’m not entirely confident. You may need someone else’s opionion