Final answer:
A solution with [OH-] = 4.6 × 10-6 M is basic.
Step-by-step explanation:
A solution with a hydroxide ion concentration, [OH-], of 4.6 × 10-6 M is considered basic. This is because in a basic solution, the hydroxide ion concentration is greater than the hydronium ion concentration, [H3O+]. The hydronium ion concentration in this solution is less than 1 × 10-7 M, which classifies it as basic.