Astronomy quiz question: hottest star

Astronomy 210 Quiz 4, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

Which star is hottest?
(A) B5 supergiant.
(B) K2 supergiant.
(C) M2 giant.
(D) O5 main sequence star.

Correct answer: (D)

Using the OBAFGKM spectral type mnemonic, or reading off of an H-R diagram (provided on this quiz), the O5 main sequence star is the hottest, followed by the B5 supergiant, K2 supergiant, and M2 giant. Possibly a few students chose the B5 supergiant "B is for blue-hot" (when in fact the O5 main sequence star would be hotter). Notably, this quiz was given the week after an OBAFGKM poetry slam.

Section 30676
(A) : 7 students
(B) : 5 students
(C) : 1 student
(D) : 28 students

"Success level": 70% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73
Exam code: quiz04s0sO