Assertion: The Harappan seal is possibly the most distinctive artefact of the Harappan or Indus Valley civilization.

Reason: We know a great deal about the lives of the Harappan people from seals alone.

The Assertion is correct but the Reason is incorrect.

The Harappan seal is possibly the most distinctive artifact of the Harappan or Indus Valley civilization. Made of a steatite stone, seals like this one often contain animal motifs and signs from a script that remains undeciphered. Yet we know a great deal about the lives of the people who lived in the region from what they left behind – their houses, pots, ornaments, tools, and seals – in other words, from archaeological evidence.

Thus, archaeological sources other than seals help us learn about the Indus Valley civilization. So, the reason given here is incorrect.