A solution has a [H3O+] of 1 × 10−3 M. What is the [OH−] of the solution? A. 11 M
B. 14 M
C. 1 × 10−14 M
D. 1 × 10−11 M

D. 1x10⁻¹¹ M

Explanation:

For any given aqueous solution the following formula is true:

1x10⁻¹⁴ = [H₃O⁺] * [OH⁻]

1x10⁻¹⁴ is the ion-product constant of water, Kw.

We input the given value of [H₃O⁺]:

1x10⁻¹⁴ = 1x10⁻³ * [OH⁻]

And solve for [OH⁻]:

[OH⁻] = 1x10⁻¹¹ M

Thus the correct answer is option D. 1x10⁻¹¹ M.