Chemistry organic help

Hi, please could I have help on question 6di, for reagent I’m confused why k2cr2o7 and sulfuric acid won’t work for the OH.
Paper: https://pmt.physicsandmathstutor.com/download/Chemistry/A-level/Past-Papers/CAIE/Paper-4/QP/November%202016%20(v1)%20QP.pdf
Markscheme: https://pmt.physicsandmathstutor.com/download/Chemistry/A-level/Past-Papers/CAIE/Paper-4/MS/November%202016%20(v1)%20MS.pdf
Thanks!

For D or for E?
For D, the only OH is already part of a COOH group - you can't oxidise a carboxylic acid with [O].
For E, the only OH is a phenol - the only way you could oxidise that would be to disrupt the benzene ring, which isn't going to happen with [O].
The correct answers rely on you knowing that phenol is a such a weak acid that is can't react with the weak base Na2CO3, whereas the carboxylic acid can - producing a visible product: CO2. Then you're expected to know that a phenol will react with Br2 - instantly decolourising it and producing a white ppt, whereas the benzene ring in ibuprofen would need a halogen carrier to react.

thank you, please could you clarify what you mean by halogen carrier, do you mean a AlCl3 catalyst?