Under what condition will the total linear momentum of a system be zero ?

Is linear momentum of any system always conserved?

Given that linear momentum of a system of particles is zero.

What is linear momentum ?

What will be the total linear momentum of a system of particles in a rotatory motion ?

A charge particle moves towards another charged particle. Under what conditions the total momentum and the total energy of the system conserved ?

What is the total momentum of the system of particle?