Ba(OH)₂ is a strong base, therefore completely ionises in the solution as follows Ba(OH)₂ --> Ba²⁺ + 2OH⁻ 1 mol of Ba(OH)₂ gives out 2 mol of OH⁻ therefore number of OH⁻ moles are twice the amount of Ba(OH)₂ moles in the solution hence, [OH⁻] = 2[Ba(OH)₂] therefore hydroxide ion concentration = 2 x 1.37 x 10⁻⁵ M [OH⁻] = 2.74 x 10⁻⁵ M coefficient = 2.74 exponent = -5
