Why do black holes have a massive force of gravity? a
They have small masses and small diameters
b
They have large masses and small diameters
c
They have large masses and large diameters
d
They have small masses and large diameters

A black hole is a region of spacetime where gravity is so strong that nothing no particles or even electromagnetic radiation such as light can escape from it.  Black holes are caused because of a supernova. A supernova is an exploding star that blasts part of the star into space.

The gravity is so strong because matter has been squeezed into a tiny space. That means, the large mass centers into the small diameter so Large mass comes in the small diameter which makes the strong gravity.

i believe that it is a exoplanet

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-