What type of column chromatography separates molecules by charge? a. size-exclusion chromatography b. affinity chromatography c. ion-exchange chromatography d. all of the above

The column chromatography that separates molecules by charge is ion-exchange chromatography (option C). This type of chromatography relies on the interaction between charged molecules (ions) and a charged resin in the column. Ions of opposite charge will be attracted to the resin and retained, while ions of the same charge will pass through the column more quickly. This allows for the separation of molecules based on their charge properties. Size-exclusion chromatography separates molecules based on size, while affinity chromatography separates molecules based on specific binding interactions, neither of which are related to charge separation. Therefore, option D (all of the above) is incorrect.