Why are some elements only created when a star explodes in a supernova

The elements formed in these stages range from oxygen through to iron. During a supernova, the star releases very large amounts of energy as well as neutrons, which allows elements heavier than iron, such as uranium and gold, to be produced. In the supernova explosion, all of these elements are expelled out into space.

Explanation: As iron accumulates in the stellar core, the fusion process no longer produces heat energy. At this point in the life of a massive star, the core collapses and the star explodes, sending all those atoms racing into space.

a high pressure system is a dense air mass that is usually cooler and drier than the surrounding air. a low pressure system is a less dense air mass that is usually wetter and warmer than the surrounding air.

in general, areas that experience high atmospheric pressure also experience fair weather. low pressure systems can cause the formation of clouds and storms. air usually flows from areas of high pressure to areas of low pressure..

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.