$(a)$ Name the instrument/device used to measure electric current in a circuit.
$(b)$ How is an ammeter connected in a circuit to measure current flowing through it?

(N/A) The instrument used to measure electric current in a circuit is called an $Ammeter$.
$(b)$ An $Ammeter$ is always connected in $series$ with the component or circuit through which the current is to be measured. This ensures that the total current flowing through the circuit passes through the $Ammeter$.