Assertion: Cunningham was unsuccessful in placing the Harappan Seal given to him by an Englishman in the correct time frame.
Reason: This was because he did not want to take much effort in discovering the History of India.

The Assertion is correct but the Reason is incorrect.

Alexander Cunningham, the first Director-General of the ASI (Archaeological Survey of India), conducted archaeological excavations in the mid-nineteenth century. At that time, archaeologists relied heavily on written texts and inscriptions to guide investigations.
Interest in later periods: Cunningham's main focus was on the archaeology of the Early Historic and later periods, ranging from the 6th century BCE to the 4th century CE. He used accounts from Chinese Buddhist pilgrims who had visited the subcontinent during the 4th to 7th centuries CE to locate early settlements.
Inscriptions and cultural value: Cunningham collected, documented and translated inscriptions found during his surveys. When he excavated sites, he primarily focused on recovering artefacts that he believed had cultural value. Harappa, being outside the scope of Early Historic cities and not mentioned by Chinese pilgrims, did not fit neatly into his framework.
Misunderstanding the age of Harappan artefacts: Although Harappan artefacts were found relatively frequently during the 19th century, Cunningham failed to recognize their true antiquity. He received a Harappan seal from an Englishman. Still, he couldn't place it within his familiar time frame because he believed Indian history began with the first cities in the Ganga Valley.