The ksp of iron(ii) hydroxide, fe(oh)2, is 4.87 × 10-17. calculate the molar solubility of this compound.

When iron hydroxide dissolves, it dissociates as follows
Fe(OH)₂ --> Fe²⁺ + 2OH⁻
molar solubility is the number of moles of solute that can be dissolved  is a 1 L solution
if molar solubility of Fe(OH)₂ is x then molar solubility of Fe²⁺ is x and OH⁻ is 2x
the solubility product constant - ksp formula is ;
ksp = [Fe²⁺][OH⁻]²
ksp = (x)(2x)²
ksp = x * 4x²
ksp = 4x³
ksp = 4.87 x 10⁻¹⁷
4x³ = 4.87 x 10⁻¹⁷
x = 2.30 x 10⁻⁶ M
molar solubility of Fe(OH)₂ is 2.30 x 10⁻⁶ M

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.