Final answer:
Considering their reduction potentials, the order from best to poorest oxidizing agent is likely Ag, Pb2+, Cr2+, Li, corresponding to the student's option 3.
Step-by-step explanation:
To arrange the substances from the best oxidizing agent to the poorest oxidizing agent (Pb2+, Cr2+, Li, Ag), we need to consider their reduction potentials. In general, elements or ions with a higher reduction potential act as stronger oxidizing agents because they have a greater tendency to gain electrons. Silver (Ag) and lead (Pb2+) are both known to have a positive reduction potential, which would make them better oxidizing agents compared to lithium (Li), which has a very negative reduction potential as it is a Group 1 metal and thus a strong reducing agent. Chromium (Cr) typically has multiple oxidation states, and since it is not specified, we cannot accurately rank it without additional information. However, Cr2+ is normally not a very strong oxidizing agent.
Without specific reduction potentials for each species in the provided context, a likely order based on general knowledge of redox chemistry would be: Ag, Pb2+, Cr2+, Li; meaning that silver is the best oxidizing agent and lithium is the poorest. This would correspond to option 3 listed by the student.