Suppose the pH of the saliva of a patient is 6.1. What is the hydrogen ion concentration (in M) of the patient's saliva? (Round your answer to seven decimal places.)
a) 1.0 × 10⁻⁶ M
b) 5.0 × 10⁻⁷ M
c) 2.5 × 10⁻⁷ M
d) 1.6 × 10⁻⁷ M