Answer : The correct option is, 12.40
Explanation : Given,
Concentration of [tex]OH^-[/tex] ion = 0.025 M
First we have to calculate the pOH.
[tex]pOH=-\log [OH^-][/tex]
[tex]pOH=-\log (0.025)[/tex]
[tex]pOH=1.6[/tex]
Now we have to calculate the pH.
[tex]pH+pOH=14\\\\pH=14-pOH\\\\pH=14-1.6=12.40[/tex]
Therefore, the pH of a solution is, 12.40