Final answer:
The question appears to contain errors, making it impossible to determine which pair of charged particles has the lowest potential energy according to Coulomb's law without the proper sign and magnitude information for each charge pair.
Step-by-step explanation:
According to Coulomb's law, the pair of charged particles with the lowest potential energy would be those with opposite charges, as they would attract each other and hence have negative potential energy. However, all the options provided in the question (a) and (d) appear to have typographical errors as they are repeated and do not specify the sign of the charges. To solve the question properly, you would need the correct charge signs as well as the charge magnitudes and distances between the charges. Coulomb's law indicates that potential energy is proportional to the product of the charges and inversely proportional to the distance between them.