An aqueous solution is found to have an H+ concentration of 2.0 x 10⁻⁴ M. What is the concentration of OH in this solution?
A. 5.0 x 10⁻¹¹ M
B. 4.0 M
C. 2.0 x 10⁻¹⁸ M
D. 2.0 x 10¹⁰ M