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Q.
Assertion : For any two sets $A$ and $B , A - B \subset B '$ Reason : If A be any set, then $A \cap A'= \phi$
Sets
Solution:
Let $x \in A-B$
$ \Rightarrow x \in A$ and $x \notin B$
$\Rightarrow x \in A$ and $x \in B'$
$\Rightarrow x \in B'$
$ \therefore A-B \subset B'$
It is true $A \cap A'=\phi $ [by complement laws]
Hence, both Assertion and Reason are correct but Reason is not a correct explanation of Assertion.