The correct option is A 132:72
We first simplify the given ratio 312:612 by converting the mixed fractions in the antecedent and the consequent.
Thus, 312:612=72:132.
Now, note that the reciprocal ratio of a:b is b:a.
⟹ Reciprocal ratio of 72:132 is 132:72.
⟹ Reciprocal ratio of 312:612 is 132:72