Final answer:
Oligopeptide A. (DDGE), with the highest number of negatively charged residues at physiological pH, will most likely be eluted first in a column with a net positive charge.
Step-by-step explanation:
The question you've asked about which oligopeptide will elute first in column chromatography at physiological pH using a stationary medium with a net positive charge involves understanding the interactions between the peptides and the charged stationary phase. At a physiological pH, which is typically around 7.4, peptides with a net negative charge will be repelled by the positively charged stationary phase and elute first, while those with a net positive or neutral charge will interact more with the phase and elute later. Analyzing the peptide sequences given, oligopeptide A (DDGE) will likely elute first as it contains the highest number of acidic (negatively charged) residues, specifically aspartic acid (D) and glutamic acid (E), which will be deprotonated and negatively charged at physiological pH. Therefore, among the options provided, oligopeptide A is expected to be found in the first fraction collected.