ISOELECTRONIC SPECIES: the ions or elements which have same number of electrons are called isoelectronic species.

Number of electrons in the given species;

ICl₂ : 53 + 2*17 = 87

ClO₂ ; 17 + 16 = 33

Therefore number of electrons is not same. Hence it cannot be isoelectronic pair.

BrO₂ : 35 + 2*8 + 1 = 52

BrF₂: 35 + 9*2 -1 = 52

Therefore number of electrons is same. Hence it is a isoelectronic pair.

ClO₂ : 17 + 16 = 33

BrF : 35 + 9 = 44

Therefore number of electrons is not same. Hence it cannot be isoelectronic pair.

CN^- : 6+7+1 = 14

O₃ : 8*3 = 24

Therefore number of electrons is not same. Hence it cannot be isoelectronic pair.

Hence the correct option is (ii).