India conducted nuclear explosions in Pokhran in which of the following years?

1974 and 1998

The correct answer is Option 3 - 1974 and 1998

In 1974 and 1998, India conducted a nuclear explosion in Pokhran.

India conducted nuclear explosions in Pokhran in the following years:

1974: India's first nuclear test was codenamed "Smiling Buddha".
1998: A series of nuclear tests known as "Pokhran-II" were conducted in Rajasthan.