Her despair began to fade when she returned to the Sorbonne to succeed her husband.
Explanation: The word "despair" refers to a feeling of complete hopelessness or deep sadness. In this context, it highlights the intense grief Marie Curie felt after her husband's tragic death. However, when she was offered the opportunity to continue his work and become a professor at the Sorbonne, it helped her regain purpose and gradually overcome her despair.