Answer:
 c Place them as close together as possible 
Step-by-step explanation:
 
Electrical potential energy between two opposite charges 
= - k Q₁ Q₂ / R , 
k is constant , Q₁ and -Q₂ are charges and distance between them is R. 
when R is least the magnitude of electrical potential will be least because of negative sign of electrical energy . The minimum value of R will be at situation when they will be as close to each other as possible . Hence third option is the right answer. The value of a negative fraction will be least when denominator will have least value.