The correct option is C aversion
The word 'propensity' refers to having an inclination or natural tendency to behave in a particular way.
Option A, scepticism refers to having a doubt as to the truth of something.
Option B, penchant refers to having a strong or habitual liking for something.
Option C, aversion refers to having a strong dislike or disclination for something.
Option D, proclivity refers to a tendency to choose or do something regularly.
Thus, according to the meaning, the word 'aversion' is the opposite of the word 'propensity'.