Why do stars explode? a. their cores collapse b. nuclear fusion takes place c. starquakes d. E=MC^2?

a. is the best answer, but it's wrong.

When stars explode (..called a supernova..) the core doesn't *always* collapse. In most supernovas, all the material surrounding the core collapses onto it and rebounds in the actual explosion but the core survives. Exceptions are neutron stars and black holes that sometimes result from supernovas.

Another example of our public school system at work (barf)

The core only collapses in a type II supernova, but as someone else had mentioned the core still remains afterward providing it does'nt collapse into a black hole.

Type Ia supernova occur due to a thermonuclear runway effect in a white dwarf (which is uncontrolled fusion).

Therefore technically a & b are both correct depending on the situation

a) type II

b) type Ia.

You will likely flunk this course because you don't want to study your text. In life, people are not going to pay you good money for regurgitating other people's answers, but for being able to build upon your level of understanding and even think beyond it.

When the explosive force in stars is greater than the gravity of the star.

A is your answer.