Answer:
Most responsible for the formation of a star is gravitational force.
Step-by-step explanation:
A fundamental force that acts between any two bodies having mass is the gravitational force. Though it is a weak force but it plays the major role in formation of the universe.
The stars are born in molecular cloud of dust and gases - the nebula. This cloud condenses under its own gravity and contracts to form the core. Further, more mass is gathered as the core starts spinning due to gravity.
When the nuclear fusion starts, the balance between the pressure and gravity holds the star together.
Thus, most responsible for the formation of a star is gravitational force.