What is the pH of a 0.030 M solution of oxalic acid? Ka for oxalic acid is 5.9 × 10−2.

Answer 1

You need to find the H+ concentration first.
https://socratic.org/questions/calculate-the-h-of-a-0-530-m-solution-of-oxalic-acid-ka-5-90-x-10-2-3-sig-figs-u

Then, the pH is easy
pH=-1ogH+