Electric field is proportional to the charge and inversely proportional to the square of distance:

With charge 2q and distance 2r, the electric field is proportional to:

The new electric field is half of that of the original measured field.
Answer:
The minimum magnetic field is 0.078 T.
Explanation:
Given that,
Current = 16 A
Side = 15 cm
Mass 
Mass each segment in given square loop is

We need to calculate the torque due to gravity
Using formula of torque


The torque due to magnetic field


The equilibrium condition

Put the value into the formula



Put the value into the formula


Hence, The minimum magnetic field is 0.078 T.
That would be the atom I believe.