The correct chemical formula for magnesium chlorate can be determined by balancing the charges of the ions involved. The magnesium ion (Mg²⁺) has a charge of +2, while the chlorate ion (ClO₃⁻) has a charge of -1.
To balance the charges, you need two chlorate ions for every magnesium ion since Mg has a +2 charge and each ClO₃ has a -1 charge. Therefore, the formula is:
Mg(ClO₃)₂
This corresponds to option A:
A. Mg(ClO₃)₂