The measured pOH of a solution is 5.5. What is the hydrogen ion, [H+ ],
concentration?

First, calculate pH using the pOH:

14 - pOH = pH --> pH = 14 - 5.5 = 9.5

[H+] = 10^-pH = 10^-9.5 = 3.2 x 10^-10 M ≈ 3 x 10^-10 M (The answer should technically only be one sig fig, since the pOH is given to only one decimal place).

beta decay is the answer