* Young stars are formed from the collapse of giant clouds of gas and dust, which are primarily composed of hydrogen and helium.
* Old stars have had time to fuse hydrogen into heavier elements like carbon, oxygen, and nitrogen through nuclear fusion. They may also have undergone further fusion to create even heavier elements.
So, what do you want to know?
* Are you asking about the types of elements?
* If so, young stars are mostly hydrogen and helium, while old stars have a greater abundance of heavier elements.
* Are you asking about the amount of elements?
* If so, this depends on the star's mass. Massive stars fuse heavier elements and "die" in supernova explosions, scattering these elements into space. These elements then become building blocks for new stars and planets. Therefore, young stars born after a supernova will have more heavy elements.
Please clarify your question so I can give you a more specific answer!
