From what i know it is c. it is a lever
The kinetic energy K given to the helium nucleus is equal to its potential energy, which is

where q=2e is the charge of the helium nucleus, and

is the potential difference applied to it.
Since we know the kinetic energy, we have

and from this we can find the potential difference:
I think the answer is c but I’m not sure
The length of a vector arrow represents an magnitude