Assume That Acid Rain Has Lowered the PH of a Particular

Assume that acid rain has lowered the pH of a particular lake to pH 4.0. What is the hydroxyl ion concentration of this lake?

A) 1 × 10⁻¹⁰ mol of hydroxyl ion per liter of lake water
B) 1 × 10⁻⁴ mol of hydroxyl ion per liter of lake water
C) 10.0 M with regard to hydroxyl ion concentration
D) 4.0 M with regard to hydroxyl ion concentration
E) both B and D