How does the metallicity (elements heavier than helium) generally compare in very old stars (Population II) compared to the Sun (Population I)?

Answer

Their metallicity is significantly lower

Stars born early in the universe had less time for stellar recycling, resulting in a chemical makeup dominated by hydrogen and helium, thus having very low metallicity.

How does the metallicity (elements heavier than helium) generally compare in very old stars (Population II) compared to the Sun (Population I)?
Elementastronomyhydrogenstarhelium