Correct option is $3$. low resistance in parallel An ammeter is always connected in series to a circuit. Since Galvanometer is a very sensitive instrument therefore it can't measure heavy currents. In order to convert a Galvanometer into an Ammeter, a very low resistance known as "shunt" resistance is connected in parallel to Galvanometer. In short To convert a galvanometer into an ammeter a low value resistance is to be connected in parallel to it called shunt.