Answer
a. NaOH is a strong base and dissociates completely into Na+ and OH-. So, the concentration of [OH-] is the same as NaOH. Therefore [OH-] = 0.25M.
b. $NH_{3}$ is a weak base and dissociates partially. Therefore [OH-] < [$NH_{3}$]
c. It is a strong base and dissociates completely. Therefore [OH-]= [$Sr(OH)_{2}$]
d. KOH is a strong base and dissociates completely. Therefore [K+] = [OH-]
Work Step by Step
a. NaOH is a strong base and dissociates completely into Na+ and OH-. So, the concentration of [OH-] is the same as NaOH. Therefore [OH-] = 0.25M.
b. $NH_{3}$ is a weak base and dissociates partially. Therefore [OH-] < [$NH_{3}$]
c. It is a strong base and dissociates completely. Therefore [OH-]= [$Sr(OH)_{2}$]
d. KOH is a strong base and dissociates completely. Therefore [K+] = [OH-]