Answer: [tex][H_3O^+]=4.0*10^-^1^1M[/tex]
Explanation: Concentration of hydroxide ion and hydronium ion are related to each other as:
[tex][H_3O^+]=\frac{1.0*10^-^1^4}{[OH^-]}[/tex]
Hydroxide ion concentration is given. So, we can plug in the value and calculate the hydronium ion concentration easily.
[tex][H_3O^+]=\frac{1.0*10^-^1^4}{2.5*10^-^4}[/tex]
[tex][H_3O^+]=4.0*10^-^1^1M[/tex]
