How are chemical elements greater than atomic mass of iron are thought to be
formed?
In the core of stars
In the core of earth
By neutron star merger
During the big bang

Chemical elements with atomic masses greater than iron (atomic mass ~55.85 u) are primarily formed through neutron star mergers via the rapid neutron capture process (r-process), where neutron-rich environments enable the synthesis of heavy nuclei like gold, platinum, and uranium.​

Option Analysis

In the core of stars
Stars fuse lighter elements up to iron through stellar nucleosynthesis, as iron fusion consumes rather than releases energy, marking the end of viable fusion chains in stellar cores. The slow neutron capture process (s-process) in asymptotic giant branch stars produces some elements slightly heavier than iron, but not the majority of very heavy ones.​

In the core of Earth
Earth’s core involves no significant nucleosynthesis; it consists of differentiated materials from pre-existing cosmic elements, with radioactive decay but no creation of new heavy elements beyond iron.​

By neutron star merger
This is the correct mechanism. Neutron star mergers eject neutron-rich matter, triggering the r-process: atomic seeds rapidly capture neutrons faster than beta decay, forming unstable heavy isotopes that decay into stable heavy elements, dispersing them into space.​

During the Big Bang
Big Bang nucleosynthesis formed only light elements up to lithium (~7Li); temperatures dropped too quickly for heavier synthesis, and no neutrons were available for capture processes.​

Nucleosynthesis Processes Explained

Stellar cores build elements via fusion until iron, beyond which energy input is required. Heavier elements demand neutron capture: s-process (slow, in stars) contributes ~50% of post-iron nuclei, while r-process (rapid, needing extreme neutron flux) forms the rest, confirmed dominant in neutron star mergers like GW170817. Supernovae contribute minimally to r-process heavy elements.​