A neutral metal atom becomes di-positive ion by losing two electrons. In the same way a neutral non-metal atom becomes uni-negative ion by gaining one electron. The formula of a compound which is formed by these two ions is

If the neutral metal atom lose two electrons to get octet then it must be IIA group element (Ex: Mg , Ca). If the non metal atom become uninegative ion by gaining one electron it should be halogen (Cl, F).

The chemical formula is $m{x}_2$

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