Step 1: What the question asks.
We place the activity of choosing a leader inside the sequence of PBL steps.
Step 2: Write the sequence.
Project identification, then plan, then time frame, then guidance, then outcome.
Step 3: Ask what each step produces.
Identification produces a topic. Planning produces tasks, roles and the team set-up. The time frame produces a schedule. Guidance produces feedback. The outcome produces the final work.
Step 4: Find the match.
A leader is a role. Roles are fixed along with tasks, so this belongs to planning.
Step 5: Rule out the others.
Choosing a topic, setting dates and giving feedback do not assign a leader.
Step 6: Conclude.
The best match is Defining a plan. This answer comes from reasoning about the stages because the paper carries no key, so the question is flagged as less certain.
Step 7: Why each wrong option fails.
Time frame setting gives dates, not people. Project identification gives a topic, and no team exists at that point. Guidance and monitoring is done after the team has started working. These three do not assign a leader, so only the planning step is left.
Final Answer:
The leader is identified while defining a plan, option 1.
\[ \boxed{1} \]