6683. He is a disinterested investigator.

✅ The correct answer is option C.
Uninterested : not interested in or concerned about something or someone.

Bored : feeling weary and impatient because one is unoccupied or lacks interest in one’s current activity.

Unbiased : showing no prejudice for or against something; impartial.

Reluctant : unwilling and hesitant; disinclined.

Disinterested : not influenced by considerations of personal advantage.

Synonym of Disinterested is Unbiased