Manipal Entrance Test 2015 Chemistry Paper

Cl2O = 2 × 17 + 16 = 42 electrons
ICl2− = 53 + 2 × 17 + 1 = 88 electrons
Cl2− = 2 × 17 + 1 = 35 electrons
IF2+=53+2×9−1=70 electrons
ClO2=17+2×8=33 electrons
ClO2=17+2×8+1=33 electrons
ClO2−=17+2×8+1=34 electrons
ClF2+=17+2×9−1=34 electrons
ClO2− and ClF2+ contain 34 electrons each.
Hence they are isoelectronic.