Check whether the following example is a null set or not

$D=\left\{x:x\in N,x^2+1=0\right\}$

Check whether the following example is a null set or not

$E=\{x:x\in W,x+3\le 3\}.$

Check whether the following example is a null set or not

Check whether the following example is a null set or not.

$G=\left\{0\right\}$

Check whether the following example is a singleton set or not

$A=\left\{x:x\in Z,x^2=4\right\}$

Check whether the following example is a singleton set or not

Check whether the following example is a singleton set or not

$A=\{x:x\in Z,|x|=1\}$

Check whether the following example is a singleton set or not

Check whether the following example is a singleton set or not

$A=\{x: x \mathrm{is} \mathrm{an} \mathrm{even} \mathrm{prime} \mathrm{number}\}$