Explanation

Pakistan conducted a series of nuclear tests on 28 May 1998

conducted at the Chagai test site, in Balochistan.

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

The tests were performed at Ras Koh Hills in the Chagai District 

it was Pakistan's first public test of nuclear weapons.

while 

Chagai II

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

The number of tests is 1