Final answer:
The statement is false; the galaxy disk mostly contains younger, metal-rich Population I stars concentrated in the spiral arms, in contrast to the older, metal-poor Population II stars in the halo.
Step-by-step explanation:
The statement that the disk of the galaxy is mostly made of old metal-poor stars is false. The disk actually contains Population I stars, which are younger and have more heavy elements than the stars found in the halo. The disk is where you find the spiral arms and generally younger stars that have been formed from gas enriched with heavier elements by previous generations of stars. For example, the Sun is a Population I star. This is in contrast to Population II stars, which are older and found in the halo and globular clusters, and are poorer in metals.