Final answer:
A polypeptide with a net positive charge at physiologic pH (~7.4) most likely contains amino acids with Basic R groups.
Step-by-step explanation:
A polypeptide with a net positive charge at physiologic pH (~7.4) most likely contains amino acids with Basic R groups. Basic amino acids such as Arginine (Arg), Lysine (Lys), and Histidine (His) have side chains that are positively charged at neutral pH, allowing the polypeptide to have a net positive charge.