After whose death did Duryodhana make Karna his army chief?

Correct option is C

• Duryodhana appointed Karna as the commander-in-chief of the Kaurava army after the death of Dronacharya on the fifteenth day of the Kurukshetra war.
  
• This transition marked the beginning of the Karna Parva in the Mahabharata. Karna led the Kaurava forces from the sixteenth day onward, facing Arjuna in intense battles until his own death on the seventeenth day.