Question

which of the following constitutes a group of the isoelectronic species?
1) C2^2- , O2^-, CO , NO 2) NO^+ , C2^2- , CN^- , N2 3) CN^- , N2, O2^2-, CO3^2- 4) N2, O2^- , NO^+ , CO

Answer 1

2) they all have 14 electrons.