Suppose a star the size of our Sun, but with mass 9.0 times as great, were rotating at a speed of 1.0 revolution every 7.0 days. If it were to undergo gravitational collapse to a neutron star of radius 13 km , losing three-quarters of its mass in the process, what would its rotation speed be

Its rotation will be 3.89x10⁴ rad/s.

Explanation:

We can find the rotation speed by conservation of the angular momentum:

  (1)

The initial angular speed is:

The moment of inertia (I) of a sphere is:

   (2)

Where m is 9 times the sun's mass and r is the sun's radius

By entering equation (2) into (1) we have:

Hence, its rotation will be 3.89x10⁴ rad/s.

I hope it helps you!                                                        

the one with the highest speed

the answer is b, have negligible mass