Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?

$\{1,2,3\}\subset A$

Which of the following are examples of the null set

$\{ y:y$ is a point common to any two parallellines $\} $

Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:

$ 8\, …….\, A $

Let $A=\{a, e, i, o, u\}$ and $B=\{a, b, c, d\} .$ Is $A$ a subset of $B ?$ No. (Why?). Is $B$ a subset of $A ?$ No. (Why?)

Consider the sets

$\phi, A=\{1,3\}, B=\{1,5,9\}, C=\{1,3,5,7,9\}$

Insert the symbol $\subset$ or $ \not\subset $ between each of the following pair of sets:

$\phi \,….\,B$