How are you able to determine if conservation of momentum occurs in each collision?

Using Newtons Second law of motion

Explanation:

Newtons Second law of motion states that the rate of change momentum of a system is directly proportional to unbalanced External force acting on it.

if we consider all colliding particles as a system we can see there is no external forces acting on the system. the forces that present here due to collision are internal forces

so As per newtons second law moment should be conserved for the colliding particles.