Answer:
b. conscience.
Step-by-step explanation:
The word "scruples" refers to the act of having any hesitation, or be reluctant to do something. This word can be used as both a noun and a verb, depending on its position and usage in a sentence.
So, when the statement talks about one's scruples acting as an obstacle, then the correct word to finish or complete the sentence is "conscience". Then, the sentence will mean that one is not reluctant to act in an unlawful way or morally wrong, thereby acting against the very nature of one's conscience, the inner feeling that helps us decide if it is right or wrong.
Thus, the correct answer is option b.