When a star collapses to form a black hole, its mass
a. decreases
b. remains the same
c. increases

When a star collapses to form a black hole, its mass increases, that is letter C. One example of this is the Big Bang Theory.  

It is by no doubt that our universe had had its own starting point but how it really started became a debate for the scientists over the past centuries. From theories such as Ekpyrotic theory, White Holes, Matrix theory, and Quantum theory, the Big Bang theory is the theory mostly accepted by scientists. According to the theory, the universe started as a singularity, that is, from a black hole under extreme gravitational pressure and expanded (instead of exploded) and cooled. Its cooling, according to the theory, is still happening now as of the moment.

An atom's smaller negative particles are at a distance from the central positive particles, so the negative particles are easier to move.