Step 1: Find P\(_1\) produced in reaction 1.
Take 100 units total: A=50, B=30, C=20. Reaction 1 needs A:B = 1:2. With 50 A, max B needed = 100, but only 30 B available. So B is limiting: 30 B reacts with 15 A to give P\(_1\) = 15 units. A remaining = 35.
Step 2: Check reaction 2 for P\(_1\).
Reaction 2 needs 4P\(_1\):3C. With 15 P\(_1\), C needed = \(rac{3}{4} imes15 = 11.25\); C available = 20. So P\(_1\) is the limiting reagent in reaction 2 and is completely exhausted. \[ oxed{P_1 ext{ will be completely exhausted}} \]