which of the following ion has same no ofelctrons in its outermost and penultimate shell..zn+2,sulphide ion,magnesium ion , tri +ve cobalt ion

Dear Student,

The electron shell orbital configuration for the elements are,

shell = K,L,M,N
Zn²⁺ = 2,8,18,5 (pen ultimate = M)
sulphide = 2,8,8  (pen ultimate = L)
magnesium ion = 2,8 (pen ultimate = K)
cobalt ion (3+ve) = 2,8,15 (pen ultimate = L)

all elements in common having outermost shell = L (common)

Regards.