Answer:
CaCl2
CaO
Al2O3
AlCl3
You can do this by swapping the values of charges on the ions as below
eg- Ca2+ - 2
Cl- - 1
Now combine 1 Ca atom and 2 Cl atoms and it will give you CaCl2
Al 3+ - 3
O2- - 2
Combine 2 atoms of Al and 3 atoms of O
Al2O3
In the case of CaO, we have to make sure that the atoms are in their simplest ratio. So although we get Ca2O2, CaO is the correct form
