Outline, with reference to pressure, how a star on the main sequence maintains its stability.

A star with a mass equal to that of the Sun moves off the main sequence. Outline the main processes of nucleosynthesis that occur in the core of this star before and after this change.

Compare the fate of the star in (b) with that of a star of much greater mass.

balance of two forces/pressures;
(balance) between radiation/pressure and gravitational force/pressure;
(radiation pressure is when) photons/radiation exert outwards force on nuclei/ particles;
(gravitational pressure is when) gravitational force between particles/layers of the star acts inwards;

whilst on the main sequence hydrogen fusion/burning to give helium;
after leaving the main sequence helium fusion/burning to give carbon;

star in (b) forms red giant, heavier star forms (red) supergiants; } (do not allow “giant”)
star in (b) forms planetary nebula, heavier star goes supernova;
star in (b) forms white dwarf, heavier star forms neutron star/black hole;

(a) There was evidence of superficial learning from the syllabus. Only a few of the best candidates wrote details of radiation and/or gravitational pressure, in response to the “outline” command term.

There was evidence in (b) [HL only] that some candidates do not read the question carefully. Better candidates clearly outlined the processes before and after moving off the main sequence. Only a few demonstrated a good understanding of the term nucleosynthesis and answered this question clearly. These candidates referred to hydrogen to helium while in the main sequence and helium to carbon after leaving the main sequence.

In (c) [HL], quite a high number of candidates outlined only the fate of a star with much greater mass and did not compare this with the fate of a star with mass equal to mass of the Sun. Candidates who understood that comparison is required, often omitted planetary nebulae. The main issue here was the superficial reading of the questions. Many responded with memorized tracts of stellar evolution and did not answer the question.