Here are some options with different shades of meaning:
General confusion:
* Confused: This is a general term for someone who is unsure or puzzled.
* Puzzled: This implies a sense of bewilderment or difficulty in understanding something.
* Perplexed: This suggests a feeling of frustration or being baffled.
* Bemused: This implies a lighthearted confusion, perhaps with a hint of amusement.
Inability to solve a problem:
* Stuck: This implies being unable to progress or find a solution.
* Frustrated: This suggests a feeling of anger or disappointment at being unable to solve something.
* At a loss: This conveys a sense of helplessness or being unable to think of an answer.
* Deadlocked: This describes a situation where progress has come to a complete halt.
Inability to answer a question:
* Unsure: This indicates a lack of certainty or confidence in the answer.
* Hesitant: This implies a reluctance or hesitation to give an answer.
* Nonplussed: This describes someone who is taken aback or surprised by a question.
To get a more specific answer, please provide more context about the situation where someone is "stumped."