This post covers the final question from 2019.
Thank you.
a. Manganese is reduced from oxidation state +7 to +2.
b. 29.55 − 3.35 = 26.20 mL.
c. 0.139 g H₂C₂O₄ × (1 mol H₂C₂O₄ / 90 g) × (2 mol MnO₄⁻ / 5 mol H₂C₂O₄) = 6.18 × 10⁻⁴ mol.
d. No. At that low concentration, the burette cannot hold enough solution to complete the titration in a single filling.
Thank you. That completes my explanations of the 2019 AP Chemistry questions.