Concept:
Melody and harmony are two different musical concepts.
In melody, notes are generally sounded one after another.
In harmony, more than one note is sounded together.
Step 1: Check Assertion (A).
The assertion says that swaras are pronounced differently in melody and many swaras are pronounced simultaneously in harmony.
This is correct.
Melody is linear, while harmony is simultaneous.
Step 2: Check Reason (R).
The reason says that one voice or instrument is sufficient for melody, but harmony requires more than one voice or instrument.
This is also correct.
Step 3: Check explanation.
The reason explains the difference between melody and harmony.
Because harmony requires simultaneous sounding, more than one voice or instrument is generally needed.
Step 4: Final conclusion.
Both Assertion and Reason are correct, and Reason explains Assertion.
Hence:
\[
\boxed{\text{(A)}}
\]