Fill in the blanks to make each of the following a true statement :

$A \cup A^{\prime}=\ldots$

Taking the set of natural numbers as the universal set, write down the complements of the following sets:

$\{ x:x$ is an odd natural number $\} $

Taking the set of natural numbers as the universal set, write down the complements of the following sets:

$\{ x:x$ is a perfect square $\} $

Let $U=\{1,2,3,4,5,6,7,8,9\}, A=\{1,2,3,4\}, B=\{2,4,6,8\}$ and $C=\{3,4,5,6\} .$ Find

$(A \cup B)^{\prime}$

Taking the set of natural numbers as the universal set, write down the complements of the following sets:

$\{x: 2 x+5=9\}$

If $n(U)$ = $600$ , $n(A)$ = $100$ , $n(B)$ = $200$ and $n(A \cap  B )$ = $50$, then $n(\bar A  \cap \bar B )$ is 

($U$ is universal set and $A$ and $B$ are subsets of $U$)