Which of the following will be the final stage in the sun’s life cycle?
a. nova stage
b. red giant stage
c. planetary nebula stage
d. black dwarf stage

B. red giant stage  

When the sun runs out of fuel-hydrogen, its atmosphere expands and it becomes a red-giant star. The Sun would leave the main-sequence stage and enter the red-giant stage in which huge pressure generated in its core pushes the atmosphere outwards making it expand and nuclear fusion reaction of heavier nuclei starts. The end stage of Sun would be formation of a white dwarf.

Thus, from the given options, correct answer is B. red giant stage  

answer; i believe the correct answer is (replication is not conservative);

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.