Concept:
Sindhu-Saraswati or Harappan culture is known for painted pottery, seals, sculpture and craft traditions.
However, direct evidence of murals on house walls is not clearly available.
Step 1: Check Assertion (A).
The assertion states that murals may have existed, but no clear evidence has been found.
This is acceptable because wall paintings have not survived as direct evidence from Harappan houses.
So, Assertion (A) is correct.
Step 2: Check Reason (R).
The Reason says that painting in Sindhu-Saraswati culture is proven through painted pottery.
This is also correct because Harappan painted pottery is well known.
Step 3: Check explanation.
Painted pottery proves that painting existed in that culture.
But it does not prove that murals existed on house walls.
So, Reason is correct but does not properly explain Assertion.
Step 4: Final conclusion.
Both statements are correct, but Reason is not the correct explanation.
Hence:
\[
\boxed{\text{(B)}}
\]