He murdered the man without any qualms of conscience.

Answer: Option A

Hesitation : the action of pausing before saying or doing something.
Pang : a sudden sharp pain or painful emotion.
Excitement : a feeling of great enthusiasm and eagerness.
Curiosity : a strong desire to know or learn something.
Qualms : an uneasy feeling of doubt, worry, or fear, especially about one's own conduct; a misgiving.

Synonym of Qualms is Hesitation