Astronomy quiz question: metal-rich main-sequence stars

Astronomy 210 Quiz 7, fall semester 2016
Cuesta College, San Luis Obispo, CA

Metals are found in the outer layers of stars that started their main-sequence lifetimes:
(A) very recently.
(B) a long time ago.
(C) in metal-poor nebulae.
(D) in distant galaxies.

Correct answer (highlight to unhide): (A)

Stars produce metals (elements heavier than hydrogen and helium) in their cores during their giant/supergiant phases, up through type Ia/II supernovae explosions. Along with their unused hydrogen, these metals are then scattered into the interstellar medium, which are then incorporated into later generations of stars. An old, early generation star will have metals only in its core, while a young, later generation star will have metals sprinkled in its outer layers as well as in the core.

Section 70158
Exam code: quiz07sAOr
(A) : 28 students
(B) : 7 students
(C) : 2 students
(D) : 0 students

Success level: 77% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.18

Section 70160
Exam code: quiz07nt70
(A) : 23 students
(B) : 1 student
(C) : 0 students
(D) : 0 students

Success level: 96% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20