Concept:
A couple consists of two equal and opposite parallel forces acting at different lines of action.
Step 1: A couple produces a turning effect but no resultant force.
Step 2: The moment of a couple depends on the magnitude of one force.
Step 3: It also depends on the perpendicular distance between the two forces.
Step 4: Therefore:
\[
\text{Moment of couple}=F\times d
\]
Step 5: Hence, the correct answer is force multiplied by perpendicular distance.
\[
\boxed{\text{Force \(\times\) Perpendicular distance}}
\]