The Fe charge is 2+ and the O charge is 2- so the ratio is 1:1
FeO
In this item, it is assume that we are to express the dissociation of the formula unit given to be FeCl₂ into its ionic components.
As seen in the chemical formula, the unit is composed of iron (Fe) and chlorine (Cl). The dissociation is written as follows;
FeCl₂ --> Fe²⁺ + Cl⁻
This equation is balanced by multiplying the appropriate component with a number that would equate the number of atoms in both sides of the equation.
<em> FeCl₂ --> Fe²⁺ + 2Cl⁻</em>
You should calculate in this way
m solute= 15g
m solution = 100g
C%= m solute/m solution *100%
C% = 15/100 *100 = 15%
C%= 15%