Assertion: The Indus Valley civilisation is also called the Harappan Civilisation.

Reasoning: Indus Valley Civilisation is named after Harappa, the first site of this Civilisation.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion

The Indus valley civilization is also called the Harappan civilization because Harappa was the first site to be excavated in the early 1920s. Later many more sites were discovered around the Indus valley which made archaeologists call it as Indus Valley civilisation.