Answer :
If the fusion rate in the core of the sun were increased but the core couldn't expand then The Sun’s core would start to cool down and the rate of fusion would decrease.
When the core of sun is increased in that scenario, the reaction rate would in fact speed up and produce more energy, but the heat would also lead to a rise in pressure. The Sun would expand because the upward pressure force would outweigh the downward gravity force.
What is fusion?
A reaction known as fusion occurs when two or more atomic nuclei unite to create new atomic and subatomic particles (neutrons or protons). Energy is released or absorbed depending on how much mass there is between the reactants and products.
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