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Let $S=\{1,2,3, \ldots, 10\}$. Suppose $M$ is the set of all the subsets of $S$, then the relation $R=\{(A, B): A \cap B \neq \phi ; A, B \in M\}$ is :
symmetric and reflexive only
reflexive only
symmetric and transitive only
symmetric only
Solution
Let $S=\{1,2,3, \ldots, 10\}$
$R=\{(A, B): A \cap B \neq \phi ; A, B \in M\}$
For Reflexive,
$M$ is subset of ' $S$ '
So $\phi \in \mathrm{M}$
for $\phi \cap \phi=\phi$
$\Rightarrow$ but relation is $\mathrm{A} \cap \mathrm{B} \neq \phi$
So it is not reflexive.
For symmetric,
$\mathrm{ARB}$
$\mathrm{A} \cap \mathrm{B} \neq \phi,$
$\Rightarrow \mathrm{BRA} \quad \Rightarrow \mathrm{B} \cap \mathrm{A} \neq \phi$,
So it is symmetric.
For transitive,
If $\mathrm{A}=\{(1,2),(2,3)\}$
$ B=\{(2,3),(3,4)\} $
$C=\{(3,4),(5,6)\}$
$ARB$ $BRC$ but $A$ does not relate to $C$
So it not transitive