Answer
pH = 1.26
Explanation
If the [H3O+] of an aqueous solution is 0.055 M, then its pH can be calculated using the pH formula below.
[tex]\begin{gathered} pH=-log[H_3O^+] \\ \\ pH=-log(0.055) \\ \\ pH=-(-1.26) \\ \\ pH=1.26 \end{gathered}[/tex]The pH of an aqueous solution of 0.055 M is 1.26