How is a light element like helium is formed in stars and how is a heavier element like gold formed by stars? Elements are not formed in stars. All elements were formed during the Big Bang and no elements have been formed since then.

Both light and heavy elements are formed only under very high energy conditions, such as a supernova.

Only light elements like helium are formed by stars. They are formed from the fusion of hydrogen nuclei. A hydrogen nucleus is made of a single proton. When protons fuse together, a new atom of helium is formed. Heavier elements like gold cannot be formed under any condition.

A light element like helium is formed by the fusion of hydrogen nuclei. A hydrogen nucleus is made of a single proton. When protons fuse together, a new atom of helium is formed. Heavier elements like gold form under very high energy conditions, such as a supernova, when helium atoms combine under enough successive collisions to form very heavy elements.