Answer:
a.They have a smaller proportion of heavy elements.
Step-by-step explanation:
As a star grows old , its metal content becomes low . Our sun is Population I star which means it is very new . Its metal content is 1.4 % . By the term metal we mean any element heavier than helium . Population II stars are older than population I stars . They will have lesser content of metal . Population III are oldest star group which have metal content as less as .015 % .