What would be the relation between velocity of gun and bullet, if the mass of gun is less than the mass of bullet?
Velocity of gun is higher than the velocity of bullet
The conservation of momentum can be applied in the case of the firing. If the momentum is constant, then mass is inversely related to the velocity.
p = m × v
v = p/m
In this case, the mass of the bullet is higher than the mass of the gun, thus the velocity of the gun is higher than the velocity of the bullet.