An unknown monoprotic carboxylic acid RCOOH is mixed in a 1:1 mole ratio with its sodium salt, Na(RC — Acids and Bases Chemistry Question

An unknown monoprotic carboxylic acid RCOOH is mixed in a 1:1 mole ratio with its sodium salt, Na(RCOO). A 1.000 g sample of this 1:1 mixture is dissolved in 50 mL water and titrated with 0.5000 M NaOH solution. The pH is measured as a function of added titrant to give the following titration curve:

Which statements are correct?
I. The molar mass of RCOOH is within 5% of 265 g mol–1.
II. The pKa of RCOOH is within 0.1 unit of 4.2.