Explanation

Pakistan conducted a series of nuclear tests on 28 May 1998 at the Chagai test site, in Balochistan.

5 Nuclear tests were conducted by Pakistan at 15:15 hrs PST on 28 May 1998.

The tests were performed at Ras Koh Hills in the Chagai District of Balochistan Province.

Chagai-I was Pakistan's first public test of nuclear weapons.

while 

Chagai-II is the codename assigned to the second atomic test conducted by Pakistan, carried out on 30 May 1998

These tests followed the Chagai-I series

The test site was Kharan Desert, Pakistan