The correct option is B Motive
Words that are similar in meaning to each other are known as 'synonyms', and words that are quite unlike each other in terms of meaning are known as 'antonyms'. In this case, we have to find the word which is NOT a synonym of the word 'reason'. Options A), B) and D) are very closely related to not just each other, but also the word 'reason' itself, and are hence ruled out - Understanding, Logic and Intelligence are all related to the rational mechanisms of reasoning we have as humans. 'Motive' itself refers to a particular drive which causes us to do something; and thus we see how the word changes the meaning of the original sentence and is thus wrong.