We have been given the pOH value, then we can calculate the pH value.
pH + pOH = 14
pOH = 9.85
pH = 14 - 9.85 = 4.15
We can calculate the hydronium ion concentration using pH value
pH = -log [H₃O⁺]
[H₃O⁺] = antilog(-pH)
we can calculate antilog of pH by writing it as 10^(-4.15)
[H₃O⁺] = antilog (-4.15)
[H₃O⁺] = 7.07 x 10⁻⁵ M
