Answer:
radius of circular path becomes doubled
Step-by-step explanation:
As the charged particle is moving in a magnetic field then it experiences a centripetal force.
So, the magnetic force is balanced by the centripetal force

where, m be the mass of charged particle, q be the charge and v be the velocity, B be the magnetic field, R be the radius of circular path.

Here we observe that the radius of the path is directly proportional to the velocity of the charged particle.
R ∝ v ..... (1)
let the new radius be R' as the velocity is doubled
R' ∝ 2 v ..... (2)
Divide equation (2) by equation (1) we get
R' = 2 R
Thus, the radius of circular path becomes doubled.