Which of the following is unchanged at the end of the cno cycle?

a. carbon-12

b. oxygen-15

c. nitrogen-13

d. the four protons

The correct option is: A. carbon-12

Explanation:

The CNO cycle, the abbreviation for the carbon-nitrogen-oxygen cycle, is a catalytic cycle by which the stars produce helium from elemental hydrogen, via a series of nuclear fusion reactions.

This cycle involves the fusion of four protons with carbon (), nitrogen isotope (), and oxygen isotope (), to give an alpha particle and two electron neutrinos and positrons.

The reaction involves the regeneration of carbon () nucleus in the last step.

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