Question 4
Two forces equal in magnitude and opposite in direction act on a body along the same line of action. What happens?
The right answer is the one marked above.
There is neither motion nor turning. The two forces cancel completely. The resultant force is zero so there is no motion, and there is no separation between the lines so there is no moment either.
This is not a couple. Two opposite forces are not enough on their own — they have to act along two different lines.