What is the concentration of OH - in pure water?

a. 1.00 x 10-7 M

c. 55.4 M

b. 0.7 M

d. 1.00 x 107 M

The answer among the choices given is option A. The concentration of OH - in pure water is 1.00 x 10^-7 M. This due to the self-ionization of water into hydroxide ions (OH-) as the base and hydronium ion (H+) as the acid. The concetration of H + is the same for the OH - resulting to a neutral pH.