(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
A is true: By the RHS congruence used in Theorem 10.2's proof, △OQP ≅ △ORP, so the two tangents subtend equal angles (∠QOP = ∠ROP) at the centre.
R is true: Exercise 10.2, Q.11 establishes that a parallelogram circumscribing a circle is a rhombus (since all four sides become equal using the equal-tangent-length property).
R does not explain A: The rhombus result is an independent application of Theorem 10.2; it does not logically lead to or explain why the two tangents subtend equal angles at the centre. Hence option (B).