At 25°C, the dissociation constant of a base, BOH, is 1.0 x 10-12. The concentration of hydroxyl ions in 0.01 M aqueous solution of the base would be :

To determine the concentration of hydroxyl ions, we need to use the dissociation constant (Kb) and the concentration of the base. The dissociation constant is given by the equation: $K_b=\frac{[O{H}^{-}][B^{+}]}{[BOH]}$. We can rearrange this equation to solve for the concentration of hydroxyl ions: $[O{H}^{-}]=\frac{K_b[BOH]}{[B^{+}]}$. Since the base is weak, we can assume that the concentration of the base is approximately equal to the initial concentration, which is 0.01 M. We can also assume that the concentration of the conjugate acid ($[B^{+}]$) is equal to the concentration of hydroxyl ions ($[O{H}^{-}]$), since the base dissociates into equal amounts of conjugate acid and hydroxyl ions. So, we have: $[O{H}^{-}]=\frac{1.0\times 10^{-12}\times 0.01}{[O{H}^{-}]}$. Simplifying this equation, we get: $[O{H}^{-}{]}^2=1.0\times 10^{-14}$. Taking the square root of both sides, we get: $[O{H}^{-}]=1.0\times 10^{-7}$. Therefore, the concentration of hydroxyl ions is $1.0\times 10^{-7}$ mol L-1.