What is true regarding ideal voltmeters?

The statement that ideal voltmeters have infinite resistance is correct. This characteristic ensures that when a voltmeter is connected across two points in a circuit, it does not draw any current. If a voltmeter had low resistance, it would allow current to flow through it, which could alter the voltage being measured. By having infinite resistance, ideal voltmeters maintain the integrity of the circuit and measure the voltage accurately without affecting the circuit behavior.

In practical applications, real voltmeters have high resistance, but they are never truly infinite. The ideal condition is a theoretical construct that helps in understanding the behavior of voltmeters in a circuit. The other options regarding low resistance, the ability to measure only AC or only DC voltage, do not represent the fundamental qualities of an ideal voltmeter. An ideal voltmeter is designed to measure both types of voltage without concern for the direction of current flow.