Question

How can you identify an ionic compound from its formula? :))

Answer 1

You need to be familiar with the most common ions, and know what compounds are made of molecules (water, organic compounds).

Most (but not all) ionic compounds have a metal element in ther formula, for instance:
NaCl ; MgO ; FeSO4 then you can identify
Na+and Cl- ; Mg2+ and O2- ; Fe2+ and (SO4)2-