Answer : 1. "revolting"
Explanation :

Rotten smell is never pleasant. Besides, ‘she’ became unconscious smelling it. So, the smell was not pleasing for sure.

The words ‘gratifying’ and ‘captivating’ are synonymous with ‘pleasing’. Hence, these words can be eliminated.

“Unappealing” is not a very strong word and consequently won’t fit here.

The context demands a very strong word as ‘she’ became ‘unconscious’ smelling the rotten odour.

Only “revolting” fits the blank appropriately both contextually and grammatically. “Revolting” means causing intense disgust; disgusting