Find the paramagnetic species among the following molecule / species.(I) F− (II) O (III) Cr3+ (IV) Sr2+

To determine which species are paramagnetic, we need to look at their electron configurations, specifically whether they have unpaired electrons. Paramagnetic species have unpaired electrons, while diamagnetic species have all their electrons paired.

(I) F−: The electron configuration of F is 1s² 2s² 2p⁵. When it gains an electron to become F−, the electron configuration becomes 1s² 2s² 2p⁶. All the electrons are paired, so F− is diamagnetic.

(II) O: The electron configuration of O is 1s² 2s² 2p⁴. There are two unpaired electrons in the 2p orbital, so O is paramagnetic.

(III) Cr³⁺: The electron configuration of Cr is [Ar] 3d⁵ 4s¹. When it loses three electrons to become Cr³⁺, the electron configuration becomes [Ar] 3d³. There are three unpaired electrons in the 3d orbital, so Cr³⁺ is paramagnetic.

(IV) Sr²⁺: The electron configuration of Sr is [Kr] 5s². When it loses two electrons to become Sr²⁺, the electron configuration becomes [Kr]. All the electrons are paired, so Sr²⁺ is diamagnetic.

So, the paramagnetic species among the given options are O and Cr³⁺.