The hydrogen ion concentration of a solution is 0.001 M. What will be the hydroxyl ion concentration of solution?

Question

$\begin{array}{1 1} (a)\; 10^{-4}\; M \\ (b)\; 10^{-11}M \\ (c)\; 10^{-6}M \\ (d)\; 10^{11}M \end{array}$