How are ionic charges used in creating chemical formulas for ionic compounds?

Explanation:

Ionic compounds are formed by the positive and negative ions but over all compounds are neutral. Because total negative charges are equal to the positive charges and cancel the effect of each other.

For example:

sodium chloride is an ionic compound. It is made up of positive ion which Na⁺ and the negative ion which Cl⁻. The negative and positive charges are equal in magnitude thus cancel the effect of each other and make the compound over all neutral.

Na⁺Cl⁻ = NaCl

Another example:

Sodium carbonate: Na₂CO₃

This compound consist of cationic part which is Na⁺ and anionic part CO₃²⁻

In this compound carbonate have -2 charge while sodium have +1 charge . In order to balance the overall charges two sodium atoms are bonded with one carbonate unit. 2Na⁺ = +2 charge

thus,

Na₂²⁽⁺¹⁾CO₃²⁻ = Na₂CO₃

the answer is option a.