Which ion has the smallest radius?

(1) O2-

(2) S2-

(3) Se2-

(4) Te2-

Option-1 (O²⁻) is the correct answer.

Explanation:

All given anions contains same charge. So, we can ignore the effect of charge on these anions.

As we know all given compounds belongs to same group (Group 6) in periodic table. And from top to bottom along the group the elements are placed as,

Oxygen O

Sulfur S

Selenium Se

Tellurium Te

Hence, moving from top to bottom along the group the number of shells increases. And with increase in number of shell the atomic or ionic radii increases. As Oxygen is present at the top of the group, therefore, it has the smallest radius due to less number of shells.