Step 1:
Tarkasamgraha accepts seven Padarthas (categories) of Vaisheshika philosophy.
\[
\boxed{\text{Assertion A is correct}}
\]
Step 2:
The seven categories are:
\[
\text{Dravya, Guna, Karma, Samanya, Vishesha, Samavaya, and Abhava}
\]
Step 3:
The Reason states that Samavaya is not accepted as a category.
This is incorrect because Samavaya is one of the accepted Padarthas.
Step 4:
Hence:
\[
\boxed{\text{A is correct but R is not correct}}
\]
Therefore, the correct answer is:
\[
\boxed{\text{(3)}}
\]