Quasar is massive luminous object in space that resides supermassive black hole in it's centre. It emits electromagnetic radiation and accreting materials into it. It is found at the core of galaxy. Its masses million to billion of solar masses.
Other hand, black hole is defined by its event horizon, singularity and an Accretion disc. Black hole can be of stellar massive, super massive and tiny size.
Neutron star is remnant death of star having solar masses 1–2 units. It composes neutrons only.Neutron stars rotate rapidly.
