Which group of elements is synthesized and ejected primarily during the supernova explosion itself?

Elements heavier than iron, such as gold and uranium.

The fusion processes occurring during the star's long life, even the layered burning up to silicon, only produce elements up to iron. The extreme energy conditions present during the final core collapse and the subsequent shockwave propagation are necessary to create elements significantly heavier than iron on the periodic table. Elements like gold, platinum, and uranium require the immense energy and neutron flux associated with the core bounce and the supernova shockwave to form through rapid neutron capture processes. These newly forged heavy elements are then scattered across the interstellar medium when the shockwave successfully breaks through the stellar surface, enriching subsequent generations of cosmic material.