In which instrument can you find metal bars that produce melodic sounds when struck?

The instrument that features metal bars which produce melodic sounds when struck is the xylophone. This instrument consists of wooden or metal bars of varying lengths, each tuned to a specific pitch. When the bars are struck with mallets, they vibrate, creating a clear and resonant sound. The arrangement of the bars is similar to that of a piano keyboard, allowing players to produce melodies as they strike the bars in sequence.

In contrast, the flute, saxophone, and trumpet are wind instruments that generate sound through the vibration of air rather than by striking. The flute produces sound through an embouchure hole, while both the saxophone and trumpet rely on reed or valve systems, respectively, to alter the pitch of the sound produced. Therefore, the xylophone is distinctly characterized by its use of mallets and metal bars, making it the correct choice for the question.