Which instrument can be used to determine if a feedline and antenna are properly matched?

A directional wattmeter is the appropriate instrument for determining if a feedline and antenna are properly matched. It measures the power that is being transmitted from the transmitter to the antenna and can also indicate how much of that power is reflected back due to impedance mismatches.

When the antenna and feedline are well-matched, most of the transmitted power is radiated by the antenna, which results in lower reflected power. When the wattmeter indicates a high level of reflected power, it suggests an impedance mismatch, indicating that the antenna system may need adjustment for optimal performance.

In contrast, a voltmeter typically measures voltage in a circuit but does not provide information regarding the relationship between transmitted and reflected power. An ohmmeter measures resistance, which does not directly indicate the matching status between the feedline and antenna. Iambic pentameter, being a form of rhythmic meter in poetry, is unrelated to radio frequency measurements and has no relevance in this context.