Calculate the $[\text{H}_3\text{O}^+]$ if pH of the solution is $4.25$

If $[\text{H}_3\text{O}^+]$ of a solution is $1 \times 10^{-4}$. What is the value of pOH at $298\,\text{K}$ ?

Calculate the molar concentration of weak monobasic acid if $K_a = 1.8 \times 10^{-5}$ and degree of dissociation is $0.01$ ?

Which of the following equimolar solutions is the best conductor of electricity at same temperature ?