The correct option is
C Falsity
The word 'veracity' indicates accuracy or conformity to facts.
Option A, purity indicates freedom from contamination.
Option B, being just refers to behaving morally right and fair.
Option C, falsity refers to the fact of being untrue, incorrect or insecure.
Option D, immorality refers to the state of being immoral, it indicates wickedness.
Thus, according to the meaning, the word 'falsity' is the most different in meaning from the word 'veracity'.