A biochemist wants to purify a protein X (molecular weight $=30.2 \mathrm{kDa}$ and $\mathrm{pI}=7.5$ ) from a solution containing proteins X and Y (molecular weight $=30.9 \mathrm{kDa}$ and $\mathrm{pI}=3.5)$ using ion exchange chromatography. In this technique, an anion exchange resin is positively charged and a cation exchange resin is negatively charged. The most appropriate resin where protein X , but not Y will remain bound is

• A

  cation exchanger at $\mathrm{pH}=7.5$.
• B

  anion exchanger at $\mathrm{pH}=2.5$.
• Correct answer
  C

  cation exchanger at $\mathrm{pH}=5.0$.
• D

  anion exchanger at $\mathrm{pH}=7.5$.

Hence, the correct answer is option: 'C'.