Question

If N = {positive integers} and subset C = {positive even integers}, what is C′?

{1, 3, 5, 7, …}

{ }

{… −7, −5, −3, −1}

{2, 4, 6, 8, …}

Answer 1

Whenever we need to compute the complement of a set, we first need to know what the "universe" is for that operation. Since you mention N={positive integers} let's assume that C' is being computed relative to that universal set.

N = { 1, 2, 3, 4, 5, ... }
C = { 2, 4, 6, 8, ... }

Thus

C' = N-C = { 1, 3, 5, 7, ... } = {positive odd integers}