Is the following a set? Justify your answer.
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In the given Venn diagram $n\left(A\right)$ is

If 

$A=\left\{x:x \text{is a natural number less than is} 6\right\}$

$B=\left\{x:x \text{is a pime number which is a divisor of} 60\right\}$

$C=\left\{x:x \text{is an odd natural number less than} 10\right\}$

$D=\left\{x:x \text{is an even natural number which is a divisor of} 48\right\}$

Then write roster form for all above sets and find $A\cup B$

If 

$A=\left\{x:x \text{is a natural number less than is} 6\right\}$

$B=\left\{x:x \text{is a pime number which is a divisor of} 60\right\}$

$C=\left\{x:x \text{is an odd natural number less than} 10\right\}$

$D=\left\{x:x \text{is an even natural number which is a divisor of} 48\right\}$

Then write roster form for all above sets and find $A-D$

If 

$A=\left\{x:x \text{is a natural number less than is} 6\right\}$

$B=\left\{x:x \text{is a pime number which is a divisor of} 60\right\}$

$C=\left\{x:x \text{is an odd natural number less than} 10\right\}$

$D=\left\{x:x \text{is an even natural number which is a divisor of} 48\right\}$

Then write roster form for all above sets and find $B\cap C$

If 

$A=\left\{x:x \text{is a natural number less than is} 6\right\}$

$B=\left\{x:x \text{is a pime number which is a divisor of} 60\right\}$

$C=\left\{x:x \text{is an odd natural number less than} 10\right\}$

$D=\left\{x:x \text{is an even natural number which is a divisor of} 48\right\}$

Then write roster form for all above sets and find $D-B$

Let $A$ be the set of vectors $a=\left(a_1,a_2,a_3\right)$ satisfying ${\left(\sum _{i=1}^3\frac{a_i}{2^i}\right)}^2=\sum _{i=1}^3\frac{a_i^2}{2^i}$. Then,