Concept:
Tyagaraja, Shyama Shastri and Muthuswami Dikshitar are known as the Trinity of Carnatic music.
They are not called the trinity of Sitar, Sarod and Pakhawaj playing.
Step 1: Check Assertion (A).
The assertion says that these three are known as the trinity of Sitar, Sarod and Pakhawaj playing.
This is incorrect.
They are the Trinity of Carnatic music.
Step 2: Check Reason (R).
Shyama Shastri is associated with the mudra ‘Shyam Krishna', and Muthuswami Dikshitar used the mudra ‘Guruguha'.
So, Reason (R) is correct.
Step 3: Final conclusion.
Assertion is incorrect, but Reason is correct.
Hence:
\[
\boxed{\text{(D)}}
\]