The Neutron-to-Proton Ratio. Hope this helps Sorry if it's wrong I'm a little rusty on Physics.
Answer:
The moment arm is 0.6 m
Explanation:
Given that,
First force 
Second force 
Distance r = 0.2 m
We need to calculate the moment arm
Using formula of torque

So, Here,

We know that,
The torque is the product of the force and distance.
Put the value of torque in the equation


Where,
=First force
=First force
=Second force
= distance
Put the value into the formula


Hence, The moment arm is 0.6 m
Positive charge=proton
Negative charge=electron
No charge/neutral=neutron
Is there more information ?