The ksp of iron(ii) carbonate, feco3, is 3.13 × 10-11. calculate the solubility of this compound in g/l.

When FeCO₃ dissolves it dissociates as follows
FeCO₃ ---> Fe²⁺ + CO₃²⁻
first we need to calculate molar solubility of compound. Molar solubility is the number of moles that will dissolve in 1 L of solution
lets take molar solubility of compound as x, then molar solubility of ions are also x
ksp is the solubility constant 
ksp = [Fe²⁺][CO₃²⁻]
3.13 * 10⁻¹¹ = [x][x]
x² = 3.13 * 10⁻¹¹
x = 5.6 * 10⁻⁶ mol/L
next we need to convert molar solubility to g/L
5.6 * 10⁻⁶ mol/L * 115.8 g/mol = 648.48 * 10⁻⁶ 
solubility = 6.48 * 10⁻⁴ g/L

It is true because i have took the test and it came out to be true