Massive stars terminate in a brilliant explosion called a

Supernova

Explanation:

A supernova explosion occurs when a high mass star ends its life cycle.

When a very massive star runs out of hydrogen used in the core for the nuclear fusion, it starts burning heavier and heavier elements (helium, carbon, etc.). However, this process stops when the star has burnt all elements lighter than iron: in fact, nuclear fusion of the iron cannot occur, since the process releases less energy than the amount of energy needed to start it. At this point, therefore, the star can no longer produce energy by nuclear fusion, and there is no longer any outward pressure that can counterbalance the gravitational force of the star, pushing inward: as a result, the star collapses under the action of gravity, and the outer layers "bounce off the core" producing a huge explosion called supernova.

The remnant of the supernova explosion is, depending on the mass of the star, a neutron star or a black hole.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.