Why in case of attraction, we take potential energy as negative and in case of repulsion we take it as positive ?

Dear student,

Potential energy is always taken to be negative of work done.

In case of attraction, no work is done in bringing an object from infinity to a certain position, so potential energy is negative.

In case of repulsion,  work is done in bringing an object from infinity to a certain position, so potential energy is positive.

Potential energy gets stored only when there is some work done.

Regards