Voltmeter should be connected always in _________ in a circuit.

A voltmeter should always be connected in parallel to the component whose voltage you want to measure. This is because a voltmeter has a very high resistance, so it does not draw any significant current from the circuit. If the voltmeter were connected in series, it would draw current from the circuit and could affect the voltage measurement.
The resistance of a voltmeter is typically in the millions of ohms, while the resistance of a typical circuit is in the ohms or even the hundreds of ohms. This means that the voltmeter will have a negligible effect on the current flow in the circuit when it is connected in parallel.