Step 1:
Purvamimamsa accepts that rituals generate an unseen potency called:
\[
\boxed{\text{Apurva}}
\]
which later produces results.
Thus, Assertion A is correct.
Step 2:
Advaita Vedanta accepts Ishwara as the dispenser of karmic results.
Thus, Reason R is also correct.
Step 3:
Reason R discusses Advaita Vedanta, whereas Assertion A concerns Purvamimamsa doctrine.
Therefore, R does not explain A.
Step 4:
Hence:
\[
\boxed{\text{Both A and R are correct, but R is not the correct explanation of A}}
\]
Therefore, the correct answer is:
\[
\boxed{\text{(2)}}
\]