Assertion: There was considerable unease in Indo-US relations during the 1950s.
Reason: India signed a 20-year Treaty of Peace and Friendship with the Soviet Union in August 1971.

Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

The correct answer is option 2: Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Assertion: There was considerable unease in Indo-US relations during the 1950s. This is correct. In the 1950s, Indo-US relations were strained due to differences over Cold War alignments, with India pursuing a non-aligned foreign policy, while the US was focused on containing communism. (correct).

Reason: India signed a 20-year Treaty of Peace and Friendship with the Soviet Union in August 1971. This is also correct. The treaty marked a closer relationship between India and the Soviet Union, particularly in the context of the Cold War. However, this treaty is not the direct cause of the unease in Indo-US relations during the 1950s, as the US’s concerns stemmed more from India's neutral stance rather than its later alignment with the Soviet Union. (correct).