Which of the Following Sets Are Isoelectronic (I

Which of the following sets are isoelectronic (i.e., have the same number of electrons) ?Br⁻, Kr, Sr²⁺C, N⁻, O²⁻Mg²⁺, Ca²⁺, Sr²⁺O²⁻, O, O²⁺Ag⁺, Cd²⁺, Pd

A) i and ii
B) i and v
C) i, iii and iv
D) ii, iii and v
E) i, iii iv and v